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

Abstract

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

Description

Technical Field

[0001] This disclosure relates to a technique for setting a forwarding schedule for allocating periods to each communication stream when multiple communication streams are forwarded separately in time. Background Technology

[0002] In IEEE 802.1Q-2018 (refer to Non-Patent Document 1), a TAS is specified as a network device for ensuring the transmission quality of each communication stream in a network where communication streams with different quality requirements coexist. TAS is short for Time-Aware Shaper.

[0003] In TAS, communication streams are stored in queues according to priority levels via network devices, and the readout control of the scheduled queues is performed based on the synchronization time within the network. Thus, each communication stream is separated and forwarded in time. The settings associated with the readout control of the scheduled queues are called the forwarding schedule.

[0004] Patent Document 1 describes a technique for setting a forwarding schedule to improve its accuracy. In Patent Document 1, network devices such as network switches and PLCs obtain the propagation delay between devices, and a network management device calculates the forwarding schedule based on the propagation delay. The network management device then distributes the calculated forwarding schedule to the network devices. PLC is short for Programmable Logic Controller.

[0005] Existing technical documents

[0006] Patent documents

[0007] Patent Document 1: Japanese Patent Application Publication No. 2022-136722

[0008] Non-patent literature

[0009] Non-patent document 1: IEEE 802.1Q-2018 - IEEE Standard for Local and Metropolitan Area Networks--Bridges and Bridged Networks. Summary of the Invention

[0010] The problem that the invention aims to solve

[0011] In Patent Document 1, the propagation delay between devices is used in the calculation of the transmission schedule. However, due to the timing deviation of the network devices sending communication streams, communication frames may not be transmitted in the expected time slots, and the expected communication bandwidth or delay may not be obtained.

[0012] The purpose of this disclosure is to make it easy to achieve the desired communication bandwidth or delay even when there is a timing deviation in the transmission of communication streams by the network device.

[0013] Methods for solving problems

[0014] The network management apparatus disclosed herein comprises: a network information acquisition unit that acquires network information representing a time update magnitude from a forwarding device, the forwarding device calculating a synchronization time and performing time synchronization based on communication frames for time synchronization, the time update magnitude being the difference between the synchronization time and an internal time managed by the forwarding device before time synchronization based on the synchronization time; a forwarding timetable calculation unit that calculates a forwarding timetable using the time update magnitude represented by the network information acquired by the network information acquisition unit, the forwarding timetable determining the period for data forwarding by the forwarding device according to each priority of the communication frames; and a timetable distribution unit that distributes the forwarding timetable calculated by the forwarding timetable calculation unit to the forwarding device.

[0015] Invention Effects

[0016] In this disclosure, a time update magnitude is used to calculate the forwarding schedule. The time update magnitude is a parameter that affects the timing deviation of the network device transmitting communication streams. Therefore, by using the time update magnitude to calculate the forwarding schedule, the desired communication bandwidth or delay can be easily achieved even when there is a timing deviation in the transmission of communication streams by the forwarding device 10. Attached Figure Description

[0017] Figure 1 This is a structural diagram of the network system 100 in Implementation Method 1.

[0018] Figure 2 This is a functional structure diagram of the transfer device 10 in Embodiment 1.

[0019] Figure 3 This is a hardware structure diagram of the transfer device 10 according to Embodiment 1.

[0020] Figure 4 This is a functional structure diagram of the network management device 20 in Implementation Method 1.

[0021] Figure 5 This is a hardware structure diagram of the network management device 20 in Implementation Method 1.

[0022] Figure 6This is a summary diagram illustrating the operation of the network system 100 in Implementation Method 1.

[0023] Figure 7 This is a flowchart of the process from receiving a communication frame containing time information for time synchronization from the transmission device 10 in Embodiment 1 to notifying the network management device 20 of the time update magnitude, etc.

[0024] Figure 8 This is an explanatory diagram illustrating the relationship between network information 51 and the forwarding schedule 52.

[0025] Figure 9 This is an illustration of the relationship between synchronization error and time slot margin.

[0026] Figure 10 This is a flowchart of the process from receiving a communication frame containing network information 51 from the network management device 20 of Embodiment 1 to distributing the forwarding schedule 52 to the forwarding device 10. Detailed Implementation

[0027] Implementation method 1. Structural description

[0028] Reference Figure 1 This describes the structure of the network system 100 in Implementation Method 1.

[0029] The network system 100 includes multiple relay devices 10, a network management device 20, a time distribution device 30, and multiple terminals 40. The multiple relay devices 10, network management device 20, time distribution device 30, and multiple terminals 40 are connected via a transmission path 90.

[0030] Each relay device 10 is a device that forwards communication frames received from an adjacent device to other adjacent devices. Specifically, each relay device 10 is a network device such as a network switch, router, hub, bridge, gateway, and 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 used for time synchronization. Each terminal 40 is a computer used by a user, etc.

[0031] Reference Figure 2 The functional structure of the transfer device 10 in Embodiment 1 will be explained.

[0032] The relay 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 relay unit 131, a time synchronization unit 132, an internal 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 amplitude calculation unit 1323.

[0033] Reference Figure 3 The hardware structure of the transfer device 10 in Embodiment 1 will be described.

[0034] The transfer device 10 includes a processor 101, a memory 102, and data communication hardware 103. The processor 101, memory 102, and data communication hardware 103 are connected via a bus 104.

[0035] Communication port 11 is implemented by data communication hardware 103.

[0036] The data processing units of the timestamp acquisition unit 12, the communication control unit 13, and the setting unit 14 are implemented by hardware, software, firmware, or a combination thereof. The software and firmware are described as programs and stored in the memory 102. When the data processing units are implemented by software or firmware, the processor 101 reads the programs from the memory 102 and executes them to operate as individual data processing units.

[0037] Reference Figure 4 This section explains the functional structure of the network management device 20 in Implementation Method 1.

[0038] 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 timetable calculation unit 25, and a transfer timetable distribution unit 26.

[0039] Reference Figure 5 This section describes the hardware structure of the network management device 20 in Implementation Method 1.

[0040] The network management device 20 includes a processor 201, a memory 202, and data communication hardware 203. The processor 201, memory 202, and data communication hardware 203 are connected via a bus 204.

[0041] Communication port 21 is implemented by data communication hardware 203.

[0042] The data processing units, including the network information acquisition unit 22, synchronization error estimation unit 23, setting unit 24, transfer schedule calculation unit 25, and transfer schedule distribution unit 26, are implemented using hardware, software, firmware, or a combination thereof. The software and firmware are described as programs and stored in memory 202. When the data processing units are implemented using software or firmware, the processor 201 reads the programs from memory 202 and executes them to perform the operations of each data processing unit.

[0043] Processors 101 and 201 refer to CPUs or system LSIs, etc. CPU stands for Central Processing Unit. LSI stands for Large Scale Integration. Processors 101 and 201 can also be referred to as processing devices, computing devices, processors, microprocessors, microcomputers, or digital signal processors.

[0044] Memory 102 and 202 refer to non-volatile or volatile semiconductor memories such as RAM, ROM, flash memory, EPROM, or EEPROM. RAM is short for Random Access Memory. ROM is short for Read Only Memory. EPROM is short for Erasable Programmable Read Only Memory. EEPROM is short for Electrically Erasable Programmable Read-Only Memory. Memory 102 and 202 can also be removable recording media such as disks, floppy disks, optical disks, compact discs, mini-disks, or DVDs. DVD is short for Digital Versatile Disc.

[0045] Data communication hardware 103 and 203 are network cards for Ethernet (registered trademark), etc.

[0046] Furthermore, the data processing units of the transfer device 10 and the network management device 20 can be implemented using dedicated hardware. Dedicated hardware can be a single circuit, a composite circuit, a programmable processor, a parallel programmable processor, an ASIC, an FPGA, or a combination thereof. ASIC stands for Application Specific Integrated Circuit. FPGA stands for Field Programmable Gate Array.

[0047] Alternatively, a portion of the data processing unit can be implemented using dedicated hardware, while the remaining portion can be implemented using the aforementioned processors 101 and 201 and memories 102 and 202.

[0048] Description of the action

[0049] Reference Figures 6 to 10 This describes the operation of the network system 100 in Implementation Method 1.

[0050] The operation steps of the network system 100 in Implementation 1 are equivalent to the transfer timetable setting method in Implementation 1.

[0051] Action summary

[0052] Reference Figure 6 This section provides an overview of the operation of the network system 100 in Implementation Method 1.

[0053] In network system 100, data forwarding is controlled according to the Transfer Schedule (TAS) specified by IEEE 802.1Q-2018. Specifically, network management device 20 sets a forwarding schedule 52 as a set of settings related to queue readout control. Each forwarding device 10 reads the queue according to the forwarding schedule 52, thereby forwarding data according to the forwarding schedule 52.

[0054] The time distribution device 30 distributes time synchronization communication frames containing time information. The time synchronization communication frames are distributed to each terminal 40 via the relay device 10. Each relay device 10 and each terminal 40 performs time synchronization based on the time information contained in the time synchronization communication frames.

[0055] During time synchronization, each relay device 10 measures the propagation delay with adjacent devices and the intra-device delay within the relay device 10. Additionally, each relay device 10 calculates a time update magnitude, which is the difference between the synchronization time calculated based on the time information during time synchronization and the internal time managed by the relay device 10 before time synchronization based on the synchronization time. Each relay device 10 sends network information 51, representing the propagation delay, intra-device delay, and time update magnitude, to the network management device 20.

[0056] The network management device 20 uses the network information 51 sent from each relay device 10 to calculate and determine a relay schedule 52 for the period during which each relay device 10 will relay data. Then, the network management device 20 distributes the relay schedule 52 to each relay device 10.

[0057] Then, each transfer device 10 transfers data within the period determined by the transfer schedule 52.

[0058] Operation of transfer device 10

[0059] Reference Figure 2 This explains the operation of the transfer device 10 in Embodiment 1.

[0060] Communication port 11 forwards the frames constituting the communication stream received from the external device to the timestamp acquisition unit 12. Additionally, communication port 11 forwards the frames constituting the communication stream received from the timestamp acquisition unit 12 to the external device.

[0061] The timestamp acquisition unit 12 forwards the communication frames received from the communication port 11 to the communication control unit 13. Additionally, the timestamp acquisition unit 12 forwards the 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 sent to the communication port 11, and notifies the communication control unit 13 of this.

[0062] In the communication control unit 13, the forwarding unit 131 forwards the communication frame received from the timestamp acquisition unit 12 to the corresponding destination communication port. If the communication frame received from the timestamp acquisition unit 12 is a time synchronization communication frame, the forwarding unit 131 forwards the communication frame to the time synchronization unit 132.

[0063] When forwarding a communication frame to a communication port, the forwarding 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 comparing the attributes of the received frame, such as the receiving port number, header information, payload information, and error information, with the pattern of the setting information received from the setting unit 14. For example, suppose the setting unit 14 is configured such that if a communication frame received through port number 1 has a destination MAC address of 12-34-56-AB-CD-EF and an EtherType of 0x0800 (IP communication), it assigns a priority of 7 and an ID of 1. In this case, the forwarding unit 131 determines whether the communication frame conforms to this setting; if it does, it assigns a priority of 7 and an ID of 1 to the communication frame.

[0064] The forwarding unit 131 stores communication frames in queues corresponding to priorities. Then, the forwarding unit 131 performs time-based queue readout control according to the Time-Scheduled Access Scale (TAS) specified in IEEE 802.1Q-2018. Here, the time in the forwarding device 10 is synchronized with other devices via the time synchronization unit 132. Thus, time-schedule forwarding is achieved, and each communication stream is separated and forwarded in time.

[0065] Here, the transfer unit 131 receives the setting value related to the readout control of the scheduled queue, namely the transfer schedule 52, from the setting unit 14. The setting unit 14 maintains two transfer schedules: the ongoing transfer schedule 52 and the transfer schedule 52 for a newly scheduled application. When the time arrives at the application time of the transfer schedule 52 for the new scheduled application, the transfer unit 131 adopts the transfer schedule 52 for the new scheduled application.

[0066] The time synchronization unit 132 performs time synchronization processing conforming to time synchronization configuration files such as PTP or gPTP based on PTP as specified by IEEE 1588. PTP is short for Precision Time Protocol. gPTP is short for Generalized PTP.

[0067] The propagation delay calculation unit 1321 exchanges the reception or transmission time of the time synchronization frame obtained by the timestamp acquisition unit 12 with the external device, and calculates the propagation delay between the external device corresponding to the time synchronization. Propagation delay is the delay in the communication flow generated on the transmission path between devices. If it is a wired network, the propagation delay is cable delay or fiber optic 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 contained in the communication frame for time synchronization distributed from the time distribution device 30. The time synchronization unit 132 synchronizes the time managed by the relay device 10, i.e., the internal time, with the calculated synchronization time.

[0068] Here, errors in obtaining the timestamp and frequency deviations between the clocks of the time distribution device 30 and the transmission device 10 are the main reasons for errors in the calculated synchronization time. Therefore, a time jump occurs when synchronizing with the synchronization time calculated by the synchronization time calculation unit 1322.

[0069] The time update amplitude calculation unit 1323 calculates the time jump, i.e. the time update amplitude, which is the difference between the time when the transfer device 10 operates autonomously before synchronizing with the time distribution device, i.e. the internal time, and the newly synchronized time, i.e. the synchronization time.

[0070] The intra-device delay calculation unit 133 calculates the delay of each communication stream within the relay unit 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 communication stream obtained by the timestamp acquisition unit 12. The intra-device delay calculation unit 133 calculates the intra-device delay for each identifier of the communication stream assigned by the relay unit 131.

[0071] The propagation delay calculated by the propagation delay calculation unit 1321, the time update magnitude calculated by the time update magnitude calculation unit 1323, and the intra-device delay calculated by the intra-device delay calculation unit 133 are sent to the notification unit 134. Regarding the propagation delay, intra-device delay, and time update magnitude, the most recent measured value, or statistical values ​​such as minimum, maximum, average, or variance over a certain period, can be notified. The notification unit 134 stores the received propagation delay, time update magnitude, and intra-device delay in a communication frame destined for the network management device 20, and sends it to an external device via the forwarding unit 131, the timestamp acquisition unit 12, and the communication port 11. Thus, the propagation delay, time update magnitude, and intra-device delay are notified to the network management device 20.

[0072] The setting unit 14 notifies the forwarding unit 131 of the maintained forwarding schedule 52 and the application time of the forwarding schedule 52. The setting unit 14 obtains and maintains the forwarding schedule 52 distributed from the network management device 20 via the communication port 11, the timestamp acquisition unit 12, and the forwarding unit 131. In addition, the setting unit 14 can also maintain a forwarding schedule 52 set by the user.

[0073] Reference Figure 7 The process of receiving a communication frame containing time information for time synchronization from the transmission device 10 of Embodiment 1 and notifying the network management device 20 of the time update magnitude, etc., will be described.

[0074] As described above, the relay device 10 receives communication frames for time synchronization. Then, the relay unit 131 forwards the communication frames for time synchronization to the time synchronization unit 132.

[0075] (Step S11: Synchronization time calculation and processing)

[0076] 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 contained in the communication frame used for time synchronization.

[0077] (Step S12: Initial calculation and judgment processing)

[0078] The synchronization time calculation unit 1322 determines whether the synchronization time calculation in step S11 is the initial synchronization time calculation.

[0079] In the case of the initial synchronization time calculation, the synchronization time calculation unit 1322 ends the processing. On the other hand, in the case of the second or subsequent synchronization time calculation, the synchronization time calculation unit 1322 causes the processing to proceed to step S13.

[0080] In the case of the initial synchronization time calculation, it is assumed that the calculated synchronization time differs significantly from the internal time managed by the transfer device 10 compared to subsequent synchronization time calculations. Therefore, in the case of the initial synchronization time calculation, the processing after step S13 is not performed, and the notification of the timing update range is stopped.

[0081] (Step S13: Time-update amplitude calculation and processing)

[0082] The time update amplitude calculation unit 1323 calculates the difference between the internal time and the synchronization time, which is the time update amplitude. That is, when the synchronization time is TM and the internal time is TS, the time update amplitude D is represented by D=TM-TS.

[0083] (Step S14: Time-to-time update amplitude notification processing)

[0084] The time update magnitude calculation unit 1323 sends the time update magnitude calculated in step S13 to the notification unit 134. Then, in addition to the time update magnitude, the notification unit 134 also sends network information 51, which represents the propagation delay sent from the propagation delay calculation unit 1321 and the intra-device delay sent from the intra-device delay calculation unit 133, to the network management device 20.

[0085] Operation of network management device 20

[0086] Reference Figure 4 This explains the operation of the network management device 20 in Implementation Method 1.

[0087] Communication port 21 forwards communication frames received from external devices to network information acquisition unit 22 and forwarding schedule distribution unit 26. Furthermore, communication port 21 forwards communication frames received from network information acquisition unit 22 and forwarding schedule distribution unit 26 to external devices.

[0088] The network information acquisition unit 22 acquires network information 51 from the communication frame forwarded from the communication port 21. When acquiring the network information 51, the network information acquisition unit 22 notifies the synchronization error estimation unit 23 of the time update magnitude shown in the network information 51, and notifies the transmission time schedule calculation unit 25 of the propagation delay and intra-device delay shown in the network information 51.

[0089] The synchronization error estimation unit 23 estimates the synchronization error as the statistical value of the time update amplitude in the most recent reference period. Specifically, the synchronization error estimation unit 23 estimates the synchronization error as the maximum value of the time update amplitude in the most recent reference period. The synchronization error estimation unit 23 also considers calculating the standard deviation of the time update amplitude in the most recent reference period and estimates the range of 2σ as the synchronization error.

[0090] The setting unit 24 maintains system specification information representing the specifications of the network system 100. The setting unit 24 notifies the transmission schedule calculation unit 25 of the system specification information. The system specification information includes topology information required for calculating the transmission schedule 52, as well as the transmission period, frame length, priority, and delay constraints of each communication stream.

[0091] The transfer schedule calculation unit 25 uses information about the synchronization error, propagation delay, intra-device delay, and system specification information maintained by the setting unit 24 for each transfer device 10 to calculate the transfer schedule 52.

[0092] Specifically, the forwarding schedule calculation unit 25 uses the synchronization error of each forwarding device 10 to set a margin before and after each time slot. A time slot is the period during which a forwarding device 10 forwards data according to the priority of each communication frame. That is, the forwarding schedule calculation unit 25 extends the synchronization error by an amount before and after the period allocated to the forwarding device 10 according to the priority of each communication frame. Then, the forwarding schedule calculation unit 25 takes into account the margin and, based on propagation delay, intra-device delay, and system specification information, searches for a combination of set values ​​that satisfy constraints such as the delay of each communication stream, thereby calculating the forwarding schedule 52.

[0093] The transfer schedule calculation unit 25 sends the transfer schedule 52 with the application time set to the transfer schedule distribution unit 26.

[0094] Reference Figure 8 The relationship between network information 51 and transmission timetable 52 is explained.

[0095] Taking into account the margin of synchronization error between the relaying devices, the relay schedule 52 is calculated based on the propagation delay between the relaying devices 10 and the intra-device delay occurring within the relaying devices 10. Specifically, there is a propagation delay X between relaying device #2 and relaying device #1. Furthermore, relaying device #2 has an intra-device delay Y. Therefore, the time slot allocated to relaying device #2 starts at a timing that is later than the time slot allocated to relaying device #1 by the propagation delay X + intra-device delay Y. And, the period obtained by adding a margin of the synchronization error Z before and after the necessary period P determined based on system specifications from this timing is allocated as the time slot for relaying device #2. The synchronization error between the relaying devices 10 affects the timing error of transmitting communication frames from the relaying devices 10. Therefore, as... Figure 8 As shown, it is preferable to set a margin for the amount of synchronization error before and after the time slot.

[0096] Reference Figure 9 This illustrates the relationship between synchronization error and time slot margin.

[0097] For each forwarding path of the communication stream, the forwarding schedule calculation unit 25 sets the maximum synchronization error as a margin in the time slot during the forwarding process. For example, in the case of forwarding device #6, since it is a forwarding path that passes through forwarding devices #1, #2 and #5, ±30ns (nanoseconds), which is the maximum synchronization error among these, is set as a margin.

[0098] The forwarding schedule distribution unit 26 distributes the forwarding schedule 52 sent by the forwarding schedule calculation unit 25 to each forwarding device 10 via the communication port 21. Then, in each forwarding device 10, the distributed forwarding schedule 52 is set in the setting unit 14, and the forwarding unit 131 uses the forwarding schedule 52 when the application time arrives.

[0099] Reference Figure 10 The process of receiving a communication frame containing network information 51 from the network management device 20 of Embodiment 1 until the forwarding schedule 52 is distributed to the forwarding device 10 will be described.

[0100] As described above, the network management device 20 receives a communication frame containing network information 51. Then, the network information acquisition unit 22 acquires the network information 51, notifies the synchronization error estimation unit 23 of the time update magnitude, and notifies the transmission schedule calculation unit 25 of the propagation delay and the intra-device delay.

[0101] (Step S21: Synchronization error estimation processing)

[0102] The synchronization error estimation unit 23 estimates the synchronization error as the statistical value of the time update magnitude in the most recent reference period. The synchronization error estimation unit 23 then notifies the transmission timetable calculation unit 25 of the estimated synchronization error.

[0103] (Step S22: Information Determination and Processing)

[0104] The transfer schedule calculation unit 25 determines whether the information required to calculate the transfer schedule 52 has been collected. The information required to calculate the transfer schedule 52 refers to the synchronization error, propagation delay, intra-device delay, and system specification information maintained by the setting unit 24 for each transfer device 10.

[0105] When the required information is collected, the timetable calculation unit 25 is transferred to proceed to step S23. On the other hand, if the required information is not collected, the timetable calculation unit 25 is transferred to end the process.

[0106] (Step S23: Margin setting process)

[0107] The transfer time calculation unit 25 uses the synchronization error estimated for each transfer device 10 to set a margin before and after each time slot.

[0108] (Step S24: Transfer schedule calculation and processing)

[0109] The transfer schedule calculation unit 25 considers the margin set in step S23 and searches for a combination of set values ​​that satisfy constraints such as delay for each communication stream based on propagation delay, intra-device delay, and system specification information. Therefore, the transfer schedule calculation unit 25 calculates the transfer schedule 52.

[0110] (Step S25: Transfer schedule distribution processing)

[0111] The transfer schedule distribution unit 26 distributes the transfer schedule 52 calculated in step S24 to each transfer device 10.

[0112] Effects of Implementation Method 1

[0113] As described above, in the network system 100 of Embodiment 1, the forwarding device 10 periodically notifies the network management device 20 of the time update magnitude with respect to the time distribution device 30. Then, the network management device 20 uses the synchronization error obtained based on the time update magnitude to set the forwarding schedule 52. Thus, even if there is a timing deviation in the transmission of the communication stream by the forwarding device 10, the desired communication bandwidth or delay can be easily achieved.

[0114] By estimating the maximum value of the time update amplitude during the most recent reference period as the synchronization error, the desired communication bandwidth or delay can be easily achieved even when there is a timing deviation in the transmission of the relay device 10. However, if the synchronization error is too large, bandwidth utilization efficiency deteriorates. By calculating the standard deviation of the time update amplitude during the most recent reference period and estimating the range of 2σ as the synchronization error, the average bandwidth utilization efficiency can be improved, and the desired communication bandwidth or delay can be achieved.

[0115] Furthermore, in the network system 100 of Embodiment 1, the process from sending network information 51 from each relay device 10 to the network management device 20 distributing the relay schedule 52 is automated. This simplifies the process of setting the relay schedule 52, reducing the cost of system implementation and operation.

[0116] Other structures

[0117] <Variation Example 1>

[0118] In Embodiment 1, the network management device 20 calculates the synchronization error based on the time update magnitude. However, each relay device 10 may also calculate the synchronization error based on the time update magnitude and notify the network management device 20. In this case, the time update magnitude calculation unit 1323 of each relay device 10 calculates the synchronization error based on the time update magnitude using the same method as the synchronization error estimation unit 23. Then, the time update magnitude calculation unit 1323 notifies the notification unit 134 of the synchronization error instead of the time update magnitude.

[0119] <Variation Example 2>

[0120] In implementation method 1, as referred to Figure 10 As explained, the forwarding schedule calculation unit 25 recalculates the forwarding schedule 52 and distributes it upon receiving network information 51. However, the forwarding schedule calculation unit 25 may also recalculate and distribute the forwarding schedule 52 in at least any of the following situations: when the timing is determined periodically, when there is a change in network information 51 beyond a certain threshold, or when data is forwarded in violation of the period determined by the forwarding schedule 52.

[0121] In the case of using periodically determined timing, the network management device 20 has a periodic timer. When the periodic timer expires, the transfer schedule calculation unit 25 recalculates and distributes the transfer schedule 52.

[0122] If there is a change of more than a baseline in the network information 51, the transfer schedule calculation unit 25 determines whether the network information 51 obtained by the network information acquisition unit 22 has changed more than a baseline compared to the previously obtained network information 51. If the transfer schedule calculation unit 25 has changed more than a baseline, it recalculates and distributes the transfer schedule 52.

[0123] If data transfer is performed outside the period specified in the transfer schedule 52, the notification unit 134 of each transfer device 10 notifies the network management device 20 of the data transfer performed outside the period specified in the transfer schedule 52. Upon receiving this notification, the transfer schedule calculation unit 25 recalculates and distributes the transfer schedule 52.

[0124] Here, "violating the period determined by the transfer schedule 52 by transferring data" refers to situations where a communication stream that is not allowed to be transferred at the current time is stored in the queue of the transfer device 10, and where the gate is closed during the process of outputting a communication stream from the transfer device 10 (when the moment when output is not allowed arrives). As to the degree of this violation, it can also be determined whether it is a violation by considering the number of violations and the number of bytes that the time slot of the violation frame exceeds.

[0125] By adopting the situation where there is a change above the reference in network information 51, or data transmission is performed in violation of the period determined by the transmission schedule 52, the reduction of the processing load on the network management device 20 and the transmission device 10 and the reduction of the used bandwidth of the network can be achieved.

[0126] In addition, the "unit" in the above description may also be replaced with "circuit", "process", "step", "processing" or "processing circuit".

[0127] The embodiments and modified examples of the present disclosure have been described above. Several of these embodiments and modified examples may be implemented in combination. In addition, any one or several of them may be implemented partially. Furthermore, the present disclosure is not limited to the above embodiments and modified examples, and various modifications can be made as needed.

[0128] Description of Reference Numerals

[0129] 100 Network system; 10 Transmission device; 11 Communication port; 12 Timestamp acquisition unit; 13 Communication control unit; 14 Setting unit; 131 Transmission unit; 132 Time synchronization unit; 133 In-device delay calculation unit; 134 Notification unit; 1321 Propagation delay calculation unit; 1322 Synchronous time calculation unit; 1323 Time update amplitude 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 Transmission schedule calculation unit; 26 Transmission schedule distribution unit; 201 Processor; 202 Memory; 203 Data communication hardware; 204 Bus; 30 Time distribution device; 40 Terminal; 51 Network information; 52 Transmission schedule; 90 Transmission path.

Claims

1. A network management device, comprising: The network information acquisition unit acquires network information representing the time update magnitude from the relaying device, which calculates the synchronization time and performs time synchronization based on communication frames used for time synchronization. The time update magnitude is the difference between the synchronization time and the internal time managed by the relaying device before time synchronization based on the synchronization time. A forwarding schedule calculation unit calculates a forwarding schedule using the time update magnitude represented by the network information obtained by the network information acquisition unit. This forwarding schedule determines the period during which the forwarding device forwards data according to the priority of each communication frame. The timetable distribution unit distributes the transfer timetable calculated by the transfer timetable calculation unit to the transfer device.

2. The network management device according to claim 1, characterized in that, The network management device further includes a synchronization error estimation unit, which estimates the synchronization error as a statistical value of the time update magnitude represented by the network information within a reference period obtained by the network information acquisition unit. The transfer schedule calculation unit uses the synchronization error estimated by the synchronization error estimation unit to calculate the transfer schedule.

3. The network management device according to claim 2, characterized in that, The forwarding schedule calculation unit calculates the forwarding schedule by extending the synchronization error by the amount before and after the period allocated to the forwarding device according to each priority of the communication frame.

4. The network management device according to any one of claims 1 to 3, wherein, The network information indicates the intra-device delay of the relay device. The transfer schedule calculation unit uses the device delay to calculate the transfer schedule.

5. The network management device according to any one of claims 1 to 4, wherein, The forwarding schedule calculation unit recalculates the forwarding schedule in at least any of the following situations: at a periodically determined time, when the network information changes beyond a certain threshold, or when data is forwarded in violation of the period determined by the forwarding schedule.

6. A forwarding device that forwards data according to a period allocated based on a forwarding schedule distributed from a network management device, the forwarding device comprising: The synchronization time calculation unit calculates the synchronization time based on the communication frames used for time synchronization. The update amplitude calculation unit calculates the difference between the synchronization time calculated by the synchronization time calculation unit and the internal time managed by the device, which is the time update amplitude; and The notification unit notifies the network management device of the time update magnitude calculated by the update magnitude calculation unit.

7. The transfer device according to claim 6, wherein, The transmission device further includes a synchronization error estimation unit, which estimates the synchronization error as the statistical value of the time update amplitude within the reference period. The notification unit will notify the network management device of the synchronization error estimated by the synchronization error estimation unit.

8. The transfer device according to claim 6 or 7, wherein, The notification unit will notify the network management device of the in-device delay of the forwarding device.

9. The transfer device according to any one of claims 6 to 8, wherein, The notification unit will notify the network management device of any instances where data transfer has occurred in violation of the period determined by the transfer schedule.

10. The transfer device according to any one of claims 6 to 9, wherein, The network management device calculates the forwarding schedule based on the time update magnitude notified by the notification unit.

11. A network system comprising a relay device and a network management device, The transfer device includes: The synchronization time calculation unit calculates the synchronization time based on the communication frames used for time synchronization. The update amplitude calculation unit calculates the difference between the synchronization time calculated by the synchronization time calculation unit and the internal time managed by the device, which is the time update amplitude; as well as The notification unit will notify the network management device of the time update magnitude calculated by the update magnitude calculation unit. The network management device includes: The forwarding schedule calculation unit uses the time update range notified by the notification unit to calculate the forwarding schedule, which determines the period during which the forwarding device forwards data according to each priority of the communication frame; as well as The timetable distribution unit distributes the transfer timetable calculated by the transfer timetable calculation unit to the transfer device.

12. A method for setting a transfer schedule, wherein, The relay device calculates the synchronization time based on the communication frames used for time synchronization. The transmitting device calculates the difference between the synchronization time and the internal time managed by the device, which is the time update amplitude. The relay device notifies the network management device of the time update magnitude. The network management device calculates a forwarding schedule using the notified time update magnitude. This forwarding schedule determines the period during which the forwarding device forwards data, according to the priority of each communication frame. The network management device distributes the forwarding schedule to the forwarding device.

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