Time synchronization device, time synchronization system, time synchronization method and program

Abstract

In a time synchronization device (100 to 400), a grandmaster selector (120) selects a first time synchronization device (100) as the grandmaster by performing a grandmaster arbitration process. A time synchronizer (130) performs time synchronization as the grandmaster when the first time synchronization device (100) is selected as the grandmaster, and performs time synchronization as a follower device when the first time synchronization device (100) is not selected as the grandmaster. An identification information memory (112) stores identification information for identifying the first time synchronization device (100) selected as the grandmaster.In a time synchronization device (200 to 400), when the first time synchronization device (100) is removed, the grandmaster selector (120) selects a second time synchronization device (200) as the new grandmaster by performing the grandmaster arbitration process. When a new time synchronization device is connected and the grandmaster selector (120) identifies the new time synchronization device as the removed first time synchronization device (100) based on the identification information, the grandmaster selector (120) reselects the first time synchronization device (100) as the grandmaster without performing the grandmaster arbitration process.

Description

Technical area

[0001] The present disclosure relates to a time synchronization apparatus, a time synchronization system, a time synchronization method and a program. background

[0002] A time synchronization system uses a standard, such as Institute of Electrical and Electronics Engineers (IEEE) 802.1AS or IEEE 1588, for master device systems that synchronize distributed clocks on a network comprising multiple devices. When the time synchronization system uses such a standard, a Best Master Clock (BMCA) algorithm is used to select a grandmaster (hereinafter referred to simply as GM) with the highest clock accuracy on the network through a grandmaster arbitration process (hereinafter referred to as GM arbitration process). The BMCA is an algorithm for selecting a device from all the devices on the network as a GM that has the highest priority level specified in BMCA priority information.Adjacent devices transmit and receive an announcement frame, which is a frame for the GM arbitration process, to and from each other to repeatedly compare BMCA priority information, which is priority information for the GM arbitration process stored in the respective device, with BMCA priority information obtained from other devices. The device with the highest priority level is selected as the GM, and the devices other than the GM, as follower devices, must synchronize a time to the time distributed by the selected GM.

[0003] In the time synchronization system, a device selected as the GM may be disconnected and removed from the network due to a problem such as a malfunction, and may be reconnected to return to the network after the problem is resolved. With such standards described above, if the GM is removed, all other follower devices must perform the GM arbitration process again using the BMCA to select a new GM. When the previous GM returns, the returned previous GM, the new GM, and all other follower devices must perform the GM arbitration process again using the BMCA to determine whether to re-select the returned previous GM. While the GM arbitration process is in progress, the devices cannot perform time synchronization with the GM. Therefore, each device must measure time.Typically, each device has a different clock accuracy and therefore a different time than other devices. Therefore, if a GM in the time synchronization system is removed and then returned, the GM arbitration process is performed, and this GM arbitration process can cause time differences between devices.

[0004] Specifically, in the time synchronization system, the GM arbitration process using the BMCA requires increasingly more time as the number of devices on the network increases. Therefore, the time differences between devices increase as the number of devices on the network increases. In the time synchronization system, when the returned GM is re-selected through the GM arbitration process using the BMCA and time synchronization is restarted between the returned previous GM and the other devices, large time differences can cause a time discontinuity, in other words, a time synchronization abnormality.

[0005] Patent Literature 1 describes, as an exemplary time synchronization system that can reduce such time synchronization abnormalities, a time synchronization system in which a master node 1B of a plurality of master nodes can be restored after being disconnected due to, for example, a failure. In Patent Literature 1, the master node 1B starts operating as a secondary master node when a master node 1A operating as a primary master node is identified among other master nodes. In Patent Literature 1, the master node 1B, as a grandmaster, transitions the state of the port to the initial state when the corrected local clock has a predetermined level of clock accuracy.In Patent Literature 1, the master node 1B determines whether to operate as a primary master node or a secondary master node using the BMCA when the local clock corrected by the master node 1B as the grandmaster clock has the predetermined level of accuracy.

[0006] Patent Literature 2 describes a communication system including communication devices that ignore the BMCA with a newly connected communication device with a high priority level unless the time difference with the newly connected communication device is smaller than a threshold. Citation listPatent literature Patent Literature 1: Unexamined Japanese Patent Application, Publication No. 2018 - 037 885 Patent Literature 2: International Publication No. WO 2020 / 059 139 Brief description of the inventionTechnical problem

[0007] In the systems described in Patent Literature 1 and 2, the GM arbitration process must be performed using the BMCA to reselect the returned previous GM, which may cause a time synchronization abnormality. Specifically, in the time synchronization system described in Patent Literature 1, when the restored master node 1B is the disconnected primary master node, the master node 1B has a predetermined level of clock accuracy, and the BMCA determines the master node 1B as the primary master node, which may cause a time synchronization abnormality. In the communication system described in Patent Literature 2, when the newly connected communication device is the returned previous GM, the BMCA is performed when the time difference with the other devices is smaller than the threshold, which may cause a time synchronization abnormality.

[0008] Under such circumstances, an objective of the present disclosure is to reduce time synchronization abnormalities resulting from the grandmaster arbitration process using the BMCA. Solution to the problem

[0009] To achieve the above object, a time synchronization device according to one aspect of the present disclosure is a time synchronization device for performing time synchronization as a grandmaster or as a follower device in a time synchronization system for synchronizing time.The time synchronization device includes a grandmaster selector that selects the grandmaster by performing a grandmaster arbitration process to identify a time synchronization device corresponding to the grandmaster from a plurality of time synchronization devices included in the time synchronization system, a time synchronizer that performs time synchronization as the grandmaster when the time synchronization device is selected as the grandmaster, and that performs time synchronization as the follower device when the time synchronization device is not selected as the grandmaster, and an identification information storage that stores identification information for identifying the one time synchronization device selected as the grandmaster.When the one time synchronization device is disconnected and removed from the time synchronization system, the grandmaster selector selects the grandmaster from the multiple time synchronization devices that do not include the one time synchronization device by performing the grandmaster arbitration process. When a new time synchronization device is connected to the time synchronization system and the grandmaster selector identifies the new time synchronization device as the removed one time synchronization device based on the identification information, the grandmaster selector selects the new time synchronization device as the grandmaster without performing the grandmaster arbitration process. Advantageous effects of the invention

[0010] The time synchronization device according to the above aspect of the present disclosure, when a new time synchronization device connected to the time synchronization system is the returned previous grandmaster, re-elects the new time synchronization device as a grandmaster without performing the grandmaster arbitration process. Therefore, the time synchronization device according to the above aspect of the present disclosure can reduce time synchronization abnormalities resulting from the grandmaster arbitration process using the BMCA more than the time synchronization device that re-elects the returned previous grandmaster after performing the grandmaster arbitration process. Short description of the drawings Fig. 1 is a schematic diagram of an overall time synchronization system according to an embodiment; Fig. 2 is a functional block diagram of the time synchronization system; Fig. 3 is a block diagram of a time synchronization device showing the hardware configuration; Fig. 4 is a diagram of an example of information stored in information memories; Fig. 5 is a flowchart of a GM selection process at system startup; Fig. Figure 6 is a flowchart of the GM selection process upon GM removal; Fig. Figure 7 is a flowchart of the GM selection process for a new connection; Fig. Figure 8 is a timing diagram of a GM removal and return control in a known time synchronization system; and Fig. 9 is a timing chart of GM removal and return control in the time synchronization system according to the present embodiment. Description of embodiments

[0011] A time synchronization system, a time synchronization device, a time synchronization method, and a program according to one or more embodiments of the present disclosure are described in detail below with reference to the drawings. Like reference numerals denote like or corresponding components throughout the drawings.

[0012] Time Synchronization System 1 According to Embodiment A time synchronization system 1 according to an embodiment of the present disclosure includes a plurality of time synchronization devices (100 to 400), each operating as a grandmaster (GM) or as a follower device on a network, and causes each follower device to synchronize time with the GM. When the time synchronization devices (100 to 400) synchronize time with each other, the clock included in each time synchronization device (100 to 400) measures the same time. In other words, in the time synchronization system 1, each of the time synchronization devices (100 to 400) shares the same time, allowing time synchronization among the plurality of time synchronization devices (100 to 400).

[0013] As in Fig. 1, a time synchronization system 1 according to the present embodiment includes, as exemplary time synchronization devices, a first time synchronization device 100, a second time synchronization device 200, a third time synchronization device 300, and a fourth time synchronization device 400. Each of the time synchronization devices 100 to 400 is a computer device, such as a server computer or a personal computer, and can transmit and receive information through a network 500. In the present embodiment, the time synchronization devices 100 to 400 are connected in a ring topology that supports multiple domains on the network 500, and perform time synchronization in both a first domain D1 and a second domain D2, which are Fig. 1. In the time synchronization system 1, if one of the time synchronization devices 100 to 400, for example, the first time synchronization device 100, is disconnected from the network 500 due to a problem such as an abnormality or a line disconnection and cannot transmit and receive information, the other time synchronization devices 200 to 400 connected to the network 500 can transmit and receive information to ensure communication redundancy.

[0014] The time synchronization devices 100 to 400 are connected in a ring topology in the present embodiment, but may also be connected in another network topology, such as a star topology or a mesh topology. As in the above embodiment, the time synchronization devices 100 to 400 may support multiple domains to ensure communication redundancy and to easily continue time synchronization. However, the time synchronization devices 100 to 400 may support a single domain without supporting multiple domains.

[0015] The time synchronization system 1 according to the present embodiment, based on a Precision Time Protocol (PTP) standard such as IEEE 802.1AS or IEEE 1588, causes the grandmaster and slave devices to transmit and receive PTP frames, such as announcement frames and sync frames, to perform time synchronization. At system startup, or specifically, when the time synchronization devices 100 to 400 are powered on, the time synchronization system 1 transmits and receives an announcement frame, which is a frame for selecting a GM, and selects a GM from the time synchronization devices 100 to 400.The time synchronization system 1 further causes the follower devices to transmit and receive PTP frames, such as Sync frames, Delay_Req frames, and Delay_Resp frames, which are time synchronization frames, to correct the time of the follower devices to the time of the grandmaster for time synchronization between the grandmaster and the follower devices.

[0016] As in Fig. As shown in FIG. 1, in the time synchronization system 1 according to the present embodiment, the above-described PTP frames are transmitted and received between the time synchronization devices 100 to 400 in both the first domain D1 and the second domain D2. In the time synchronization system 1, the first time synchronization device 100 with the highest clock accuracy is selected as the GM, and the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400, as the follower devices, perform time synchronization with the first time synchronization device 100 selected as the GM in both the first domain D1 and the second domain D2.

[0017] Time synchronization devices 100 to 400 according to the embodiment As in Fig. As shown in Figure 2, the first time synchronization device 100 includes an information storage 110 that stores information, a grandmaster selector 120 (hereinafter referred to as GM selector 120) that selects the GM, a time synchronizer 130 that performs time synchronization as the GM or as the follower device, and a time difference calculator 140 that calculates a time difference. The first time synchronization device 100 further includes a network connection controller 150 that controls a connection to the network 500, an information transmitter 160 that transmits information, and an information receiver 170 that receives information.The information memory 110 includes a priority information memory 111 that stores priority information (described later), an identification information memory 112 that stores identification information (described later), and an arbitration priority information memory 113 that stores arbitration priority information (described later).

[0018] Similar to the first time synchronization device 100, the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400 each include the information memory 110, the priority information memory 111, the identification information memory 112, the arbitration priority information memory 113, the GM selector 120, the time synchronizer 130, the time difference calculator 140, the network connection controller 150, the information transmitter 160, and the information receiver 170. Hardware configuration of time synchronization devices 100 to 400 according to the embodiment

[0019] As in Fig. 3, the first time synchronization device 100 includes, for example, a controller 51 that performs processes based on a control program 59. The controller 51 includes a central processing unit (CPU). Based on the control program 59, the controller 51 functions, for example, as the GM selector 120, the time synchronizer 130, the time difference calculator 140, and the network connection controller 150, which in Fig. 2 are shown.

[0020] Referring again to Fig. 3, the first time synchronization device 100 includes a main memory 52 into which the control program 59 is to be loaded. The main memory 52 is used as a work area for the controller 51. The main memory 52 includes a random access memory (RAM).

[0021] The first time synchronization device 100 includes an external memory 53 that prestores the control program 59. The external memory 53 provides information stored in the program to the controller 51 as instructed by the controller 51 and stores information provided by the controller 51. The external memory 53 includes a non-volatile recording medium, such as a read-only memory (ROM), a flash memory, a hard disk drive (HDD), or a solid-state drive (SSD). The external memory 53 functions, for example, as the information memory 110, the priority information memory 111, the identification information memory 112, and the arbitration priority information memory 113, which are stored in Fig. 2 are shown.

[0022] Referring again to Fig. 3, the first time synchronization device 100 includes an operating device 54 that can be operated by a user. Information input by the operating device 54 is provided to the controller 51. The operating device 54 includes information input components, such as a keyboard, a mouse, and a touchscreen.

[0023] The first time synchronization device 100 further includes a display 55 that displays information input by the operating device 54 and information output from the controller 51. The display 55 includes a display device such as a liquid crystal display (LCD) or an organic light-emitting diode (OLED) display.

[0024] The first time synchronization device 100 further includes a transceiver 56 that transmits and receives information. The transceiver 56 includes an information communication device, such as a communication network terminal or a wireless communication device connected to a network. The transceiver 56 functions as the information transmitter 160 and the information receiver 170, which are Fig. 2 are shown.

[0025] Referring again to Fig. 3, in the first time synchronization device 100, the main memory 52, the external memory 53, the operating device 54, the display 55 and the transceiver 56 are connected to the controller 51 by an internal bus 50.

[0026] The first time synchronization device 100 implements the functions of the components 110 to 113 and 120 to 170, which are described in Fig. 2, with the controller 51 using the main memory 52, the external memory 53, the operating device 54, the display 55, and the transceiver 56 as resources. For example, the first time synchronization device 100 causes the information memory 110 to store information, the priority information memory 111 to store priority information, the identification information memory 112 to store identification information, and the arbitration priority information memory 113 to store arbitration priority information.The first time synchronization device 100 further causes, for example, the GM selector 120 to perform GM selection, the time synchronizer 130 to perform time synchronization, the time difference calculator 140 to perform time difference calculation, the network connection controller 150 to perform network connection control, the information transmitter 160 to perform information transmission, and the information receiver 170 to perform information reception.

[0027] The second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400 each have the same hardware configuration as the first time synchronization device 100. Specifically, the same hardware configuration described above applies to the second time synchronization device 200 by replacing the first time synchronization device 100 with the second time synchronization device 200, to the third time synchronization device 300 by replacing the first time synchronization device 100 with the third time synchronization device 300, and to the fourth time synchronization device 400 by replacing the first time synchronization device 100 with the fourth time synchronization device 400. Therefore, the hardware configurations of the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400 will not be described in detail to avoid redundancy. Details of the functional configuration of the time synchronization devices 100 to 400 according to the embodiment

[0028] Referring again to Fig. 2, the priority information memory 111 stores priority information indicating a priority level prespecified for each of the time synchronization devices 100 to 400 based on clock accuracy. For example, the first time synchronization device 100 has priority information PrA, the second time synchronization device 200 has priority information PrB, the third time synchronization device 300 has priority information PrC, and the fourth time synchronization device 400 has priority information PrD. As shown in Fig. 4, in this case, the priority information memory 111 in the first time synchronization device 100 stores PrA = 1, the priority information memory 111 in the second time synchronization device 200 stores PrB = 2, the priority information memory 111 in the third time synchronization device 300 stores PrC = 3, and the priority information memory 111 in the fourth time synchronization device 400 stores PrD = 4. Smaller values of the priority information PrA, PrB, PrC, and PrD indicate higher priority levels of being GM. Therefore, the first time synchronization device 100 has the highest priority level of being GM, the second time synchronization device 200 has the second highest priority level, the third time synchronization device 300 has the third highest priority level, and the fourth time synchronization device 400 has the lowest priority level.

[0029] Referring again to Fig. 2, each identification information memory 112 stores identification information for identifying the time synchronization device selected as the GM. For example, the first time synchronization device 100 has identification information PrTM_A, the second time synchronization device 200 has identification information PrTM_B, the third time synchronization device 300 has identification information PrTM_C, and the fourth time synchronization device 400 has identification information PrTM_D.At the start of the time synchronization system 1, the identification information memory 112 in the first time synchronization device 100 stores PrTM_A = 1, the identification information memory 112 in the second time synchronization device 200 stores PrTM_B = 2, the identification information memory 112 in the third time synchronization device 300 stores PrTM_C = 3, and the identification information memory 112 in the fourth time synchronization device 400 stores PrTM_D = 4. In other words, at the start of the time synchronization system 1, the values of the identification information PrTM_A, PrTM_B, PrTM_C, and PrTM_D are equal to the respective values of the priority information PrA, PrB, PrC, and PrD.

[0030] When a GM selection process using a Best Master Clock Algorithm (BMCA) is performed at system startup as an example of a GM arbitration process (described later) and the first time synchronization device 100 is selected as the GM, the identification information memory 112 in the first time synchronization device 100 stores PrTM_A = 1, as shown in Fig. 4, the identification information memory 112 in the second time synchronization device 200 stores PrTM_B = 1, the identification information memory 112 in the third time synchronization device 300 stores PrTM_C = 1, and the identification information memory 112 in the fourth time synchronization device 400 stores PrTM_D = 1, as shown in Fig. 4. In other words, the respective value of the identification information PrTM_A, PrTM_B, PrTM_C, and PrTM_D stored in the corresponding identification information memory 112 in the time synchronization devices 100 to 400 is equal to the value 1 of the priority information PrA of the first time synchronization device 100 selected as the GM. Therefore, PrTM_A = PrTM_B = PrTM_C = PrTM_D = PrA = 1.

[0031] Referring again to Fig. 2, the arbitration priority information memory 113 stores arbitration priority information used to perform the GM arbitration process (described later), which indicates the priority level of the corresponding time synchronization device. For example, the first time synchronization device 100 has arbitration priority information GM_PrA, the second time synchronization device 200 has arbitration priority information GM_PrB, the third time synchronization device 300 has arbitration priority information GM_PrC, and the fourth time synchronization device 400 has arbitration priority information GM_PrD. As shown in Fig. 4, in this case, the arbitration priority information memory 113 in the first time synchronization device 100 stores GM_PrA = 1, the arbitration priority information memory 113 in the second time synchronization device 200 stores GM_PrB = 2, the arbitration priority information memory 113 in the third time synchronization device 300 stores GM_PrC = 3, and the arbitration priority information memory 113 in the fourth time synchronization device 400 stores GM_PrD = 4. In other words, the values of the arbitration priority information GM_PrA, GM_PrB, GM_PrC, and GM_PrD are equal to the respective values of the priority information PrA, PrB, PrC, and PrD.

[0032] In the present embodiment, the values of the arbitration priority information GM_PrA, GM_PrB, GM_PrC, and GM_PrD are equal to the respective values of the priority information PrA, PrB, PrC, and PrD. However, the values may be different. For example, the values of the arbitration priority information GM_PrA, GM_PrB, GM_PrC, and GM_PrD stored in the respective arbitration priority information memories 113 in the time synchronization devices 100 to 400 may simply be different from each other. In particular, the values may indicate station numbers, Internet Protocol (IP) addresses, or clock identifications (IDs).

[0033] Referring again to Fig. 2, the GM selector 120 can perform the GM arbitration process to identify a time synchronization device (100) corresponding to the GM from the time synchronization devices 100 to 400 to select the GM. At the startup of the time synchronization system 1, in other words, when the time synchronization devices 100 to 400 are each turned on at the same time and a GM has yet to be selected, the GM selector 120 performs the GM selection process using the BMCA at system startup to select a new GM. Specifically, the GM selector 120 causes the information transmitter 160 and the information receiver 170 to transmit and receive an announcement frame containing the arbitration priority information (GM_PrA, GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device to and from adjacent time synchronization devices (100 to 400).The GM selector 120 then repeatedly compares the values of the arbitration priority information (GM_PrA, GM_PrB, GM_PrC and GM_PrD) and selects the first time synchronization device 100 with the smallest value 1 as the GM. The GM selector 120 in each of the time synchronization devices 200 to 400 updates the value of the identification information PrTM_B, PrTM_C, or PrTM_D stored in the identification information memory 112 in the second time synchronization device 200, the third time synchronization device 300, or the fourth time synchronization device 400 to the same value as the identification information PrTM_A of the first time synchronization device 100. Thus, each value of the identification information PrTM_B, PrTM_C, and PrTM_D of the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400 is PrTM_B = PrTM_C = PrTM_D = PrTM_A = 1.

[0034] When the first time synchronization device 100 as the GM is disconnected and removed from the network 500 due to a problem such as an abnormality or a line disconnection, the GM selectors 120 perform the GM selection process using the BMCA upon GM disconnection to select a new GM from the time synchronization devices 200 to 400 not including the first time synchronization device 100. Specifically, the GM selector 120 in each of the time synchronization devices 200 to 400 causes the information transmitter 160 and the information receiver 170 to transmit and receive an announcement frame containing the arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device to and from adjacent time synchronization devices (200 to 400).The GM selector 120 in each of the time synchronization devices 200 to 400 then repeatedly compares the values of the arbitration priority information (GM_PrB, GM_PrC, and GM_PrD) to select the second time synchronization device 200 with the minimum value of 2 as the new GM. The GM selector 120 in each of the time synchronization devices 200 to 400 does not update the value of the identification information PrTM_B, PrTM_C, or PrTM_D in the identification information memory 112 in the respective time synchronization device 200 to 400. Specifically, the value of the identification information PrTM_B, PrTM_C, or PrTM_D of the respective time synchronization device 200 to 400 remains PrTM_B = PrTM_C = PrTM_D = 1 after the second time synchronization device 200 is selected as the new GM.

[0035] When a new time synchronization device is connected to the network 500 while the second time synchronization device 200 is performing time synchronization as the new GM, and the GM selectors 120 identify the new time synchronization device as the remote first time synchronization device 100 based on the identification information, the GM selectors 120 select the first time synchronization device 100 as the GM without performing the GM arbitration process using the BMCA. Specifically, when a new time synchronization device is connected to the network 500, the network connection controller 150 in the new time synchronization device causes the information transmitter 160 to transmit an announcement frame containing identification information to adjacent time synchronization devices (200 to 400).If the new time synchronization device is the first time synchronization device 100, the GM selector 120 in each of the time synchronization devices 200 to 400 causes the information receiver 170 to receive an announcement frame containing the identification information PrTM_A of the first time synchronization device 100 and determines that a new time synchronization device is connected to the network 500. When the value of the identification information PrTM_A included in the received announcement frame is equal to the value of the identification information PrTM_B, PrTM_C, and PrTM_D stored in the identification information memory 112 in the respective time synchronization device 200 to 400, the GM selector 120 in the respective time synchronization device 200 to 400 selects the first time synchronization device 100 as GM again without performing the GM arbitration process.The GM selector 120 in each time synchronization device 200 to 400 then notifies the first time synchronization device 100 that the first time synchronization device 100 is connected to the network 500 as a new GM, and transmits to the second time synchronization device 200, which is the current GM, a PTP frame transmission restart message indicating that the first time synchronization device 100 is connected to the network 500 as a new GM.

[0036] The GM selectors 120 do not select a new GM when a new time synchronization device is connected to the network 500 while the second time synchronization device 200 is performing time synchronization as the new GM, and the GM selectors 120 identify that the new time synchronization device is not the remote first time synchronization device 100 based on the identification information. Specifically, the GM selector 120 in the respective time synchronization devices 200 to 400 does not select a new GM if the value of the identification information included in the received announcement frame is different from the values of the identification information PrTM_B, PrTM_C, and PrTM_D stored in the identification information memories 112 in the time synchronization devices 200 to 400. Therefore, the second time synchronization device 200 continues to perform time synchronization as the GM.

[0037] If the second time synchronization device 200 continues to perform time synchronization as the GM, and the value of the identification information included in the received announcement frame is greater than the value of the identification information PrTM_B, PrTM_C, or PrTM_D stored in the identification information memory 112 in the respective time synchronization devices 200 to 400, the network connection controller 150 in the respective time synchronization devices 200 to 400 starts transmitting and receiving information to and from the new time synchronization device after time synchronization is performed between the second time synchronization device 200 as the current GM and the new time synchronization device. Therefore, the new time synchronization device can perform time synchronization as a follower device in the time synchronization system 1.

[0038] If the second time synchronization device 200 continues to perform time synchronization as the GM and the value of the identification information included in the received announcement frame is smaller than the value of the identification information PrTM_B, PrTM_C, or PrTM_D stored in the identification information memory 112 in the respective time synchronization device 200 to 400, the network connection controller 150 in the respective time synchronization device 200 to 400 does not start transmission and reception of information to and from the new time synchronization device and causes the network connection controller 150 in the new time synchronization device to disconnect from the network 500. Therefore, the new time synchronization device does not perform time synchronization as a follower device in the time synchronization system 1.

[0039] The time difference calculator 140 compares the time of the current GM with the time of the respective time synchronization device to calculate the time difference. Specifically, the time difference calculator 140 causes the information transmitter 160 and the information receiver 170 to transmit and receive PTP frames, such as Sync frames, Delay_Req frames, and Delay_Resp frames, to and from adjacent time synchronization devices (100 to 400), and calculates the time difference.

[0040] For example, the time difference calculator 140 calculates the time difference when the time synchronizer 130 performs time synchronization as a follower device. For example, when the first time synchronization device 100 is reconnected to the network 500 while the second time synchronization device 200 is performing time synchronization as the new GM, the time difference calculator 140 in the first time synchronization device 100 calculates a time difference between the time of the second time synchronization device 200 and the time of the first time synchronization device 100 before performing time synchronization as a new GM to determine whether to perform time synchronization with the second time synchronization device 200.

[0041] If selected as GM, the time synchronization device as GM causes the time synchronizer 130 to perform time synchronization. If not selected as GM, the time synchronization device as a follower device causes the time synchronizer 130 to perform time synchronization. For example, if a time synchronization device as a follower device causes the time synchronizer 130 to perform time synchronization, the time synchronizer 130 corrects the time of the corresponding time synchronization device using the time difference calculated by the time difference calculator 140 to synchronize the time with the GM.

[0042] While the second time synchronization device 200 is performing time synchronization as the new GM, the first time synchronization device 100 may be reconnected and selected as a new GM. In this case, if the calculated time difference is less than or equal to 30 seconds, which is an example of a predetermined threshold, the first time synchronization device 100, as the new GM, causes the time synchronizer 130 to perform time synchronization without performing time synchronization with the second time synchronization device 200. Therefore, the other time synchronization devices 200 and 300, which are follower devices, cause the respective time synchronizers 130 to perform time synchronization with the first time synchronization device 100, which has not performed time synchronization after connecting to the network 500.In this case, if the calculated time difference is greater than 30 seconds, which is an example of the threshold, the first time synchronization device 100, as the new GM, causes the time synchronizer 130 to perform time synchronization after performing time synchronization with the second time synchronization device 200. Therefore, the other time synchronization devices 200 and 300, which are follower devices, cause the respective time synchronizers 130 to perform time synchronization with the first time synchronization device 100, which performed time synchronization after connecting to the network 500. Flowchart of a GM selection process at system startup according to the present embodiment

[0043] The operation of each of the time synchronization devices 100 to 400 for selecting a GM at the start of the time synchronization system 1 will now be described with reference to the Fig. 5. As soon as they are switched on, each of the time synchronization devices 100 to 400 starts to Fig. 5 to perform the GM selection process at system startup. As shown in Fig. 5, the GM selector 120 first causes the information transmitter 160 to transmit an announcement frame containing arbitration priority information (GM_PrA, GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device to adjacent time synchronization devices (100 to 400) (step S101), and causes the information receiver 170 to receive an announcement frame from the adjacent time synchronization devices (100 to 400) (step S102).

[0044] After the announcement frame is received, the GM selector 120 determines whether the value of the arbitration priority information (GM_PrA, GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device is greater than the value indicating the priority level contained in the received announcement frame (step S103). If the value of the arbitration priority information (GM_PrA, GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device is larger (Yes in step S103), the GM selector 120 determines that the corresponding time synchronization device is a follower device and determines whether the value of the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) of the corresponding time synchronization device is larger than the value indicating the priority level included in the received announcement frame (step S104).

[0045] If the value of the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) of the corresponding time synchronization device is greater than the value indicating the priority level and included in the received announcement frame (Yes in step S104), the GM selector 120 updates the value of the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) of the corresponding time synchronization device to the value indicating the priority level and included in the received announcement frame (step S105), and causes the information transmitter 160 to transmit an announcement frame containing the value of the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) of the corresponding time synchronization device to adjacent time synchronization devices (100 to 400) (step S106).When the value of the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) of the corresponding time synchronization device is smaller than the value indicating the priority level included in the received announcement frame (No in step S104), the GM selector 120 performs the processing in step S106 without updating the value of the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) of the corresponding time synchronization device, and transmits an announcement frame.

[0046] If the value of the arbitration priority information (GM_PrA, GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device is less than or equal to the value indicating the priority level included in the received announcement frame (No in step S103), the GM selector 120 determines that the corresponding time synchronization device may be a GM and does not update the value of the identification information (PrTM_B, PrTM_C, PrTM_D, or PrTM_A) of the corresponding time synchronization device, and causes the announcement frame containing the arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device to be retransmitted to the adjacent time synchronization devices (100 to 400) (step S107).

[0047] After the announcement frame is transmitted, the GM selector 120 determines whether the value of the arbitration priority information (GM_PrA, GM_PrB, GM_PrC, or GM_PrD) contained in the received announcement frame is equal to the values in the other time synchronization devices and whether a GM is selected (step S108). If no GM is selected (No in step S108), the GM selector 120 returns to step S102 and repeats the processing in steps S102 to S108 until a GM is selected. If a GM is selected (Yes in step S108), the GM selection process ends at system startup. Flowchart of the GM selection process upon GM removal according to the present embodiment

[0048] The operation of each of the time synchronization devices 200 to 400 for selecting a new GM upon removal of the first time synchronization device 100, which is the GM, will now be described with reference to the Fig. 6. After a predetermined period since the last reception of a sync frame from the first time synchronization device 100, each of the time synchronization devices 200 to 400 starts the Fig. 6 shown GM selection process upon removal of the GM. As in Fig. 6, the GM selector 120 first causes the information transmitter 160 to transmit an announcement frame containing arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device to the adjacent time synchronization devices (200 to 400) (step S201), and causes the information receiver 170 to receive an announcement frame from the adjacent time synchronization devices (200 to 400) (step S202).

[0049] After the announcement frame is received, the GM selector 120 determines whether the value of the arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device is greater than the value of the arbitration priority information (GM_PrC, GM_PrD, or GM_PrB) included in the received announcement frame (step S203). If the value of the arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device is greater than the value of the arbitration priority information included in the received announcement frame (Yes in step S203), the GM selector 120 determines that the corresponding time synchronization device is a follower device and causes the information transmitter 160 to transmit the received announcement frame to the adjacent time synchronization devices (200 to 400) (step S204).If the value of the arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device is smaller than the value of the arbitration priority information (GM_PrC, GM_PrD, or GM_PrB) included in the received announcement frame (No in step S203), the GM selector 120 determines that the corresponding time synchronization device may be a GM and causes the announcement frame containing the arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) of the corresponding time synchronization device to be retransmitted to the adjacent time synchronization devices (200 to 400) (step S205).

[0050] After the announcement frame is transmitted, the GM selector 120 determines whether the value of the arbitration priority information (GM_PrB, GM_PrC, or GM_PrD) contained in the received announcement frame is equal to the values in the other time synchronization devices and whether a GM is selected (step S206). If no GM is selected (No in step S206), the GM selector 120 returns to step S202 and repeats the processing in steps S202 to S206 until a GM is selected. If a GM is selected (Yes in step S206), the GM selection process ends upon removal of the GM. Flowchart of the GM selection process for new connection according to the present embodiment

[0051] The operation for selecting a GM when a new time synchronization device is connected to the network 500 while the second time synchronization device 200 is performing time synchronization as a new GM will now be described with reference to the Fig. 7. When a new time synchronization device is connected to the network 500 and transmits an announcement frame, the Fig. 7 shows the GM selection process for new connections. As in Fig. 7, the GM selector 120 first causes the information receiver 170 to receive an announcement frame from the new time synchronization device (step S301), and then determines whether the value of the identification information contained in the received announcement frame is equal to the value of the identification information (PrTM_B, PrTM_C, or PrTM_D) stored in the identification information memory 112 (step S302).

[0052] If the values of the identification information are not equal (No in step S302), the GM selector 120 determines that the new time synchronization device is not the remote first time synchronization device 100 and does not select the new time synchronization device as the new GM. The network connection controller 150 determines whether the value of the identification information in the received announcement frame is greater than the value of the stored identification information (PrTM_B, PrTM_C, or PrTM_D) (step S303). If the value of the identification information contained in the received announcement frame is greater (Yes in step S303), the network connection controller 150 starts transmitting and receiving information to and from the new time synchronization device (step S304) after the new time synchronization device performs time synchronization, and terminates the GM selection process upon reconnection.If the value of the identification information included in the received announcement frame is smaller (No in step S303), the network connection controller 150 terminates the GM selection process upon new connection without starting transmission and reception of information to and from the new time synchronization device.

[0053] If the values of the identification information are the same (Yes in step S302), the GM selector 120 determines that the new time synchronization device is the remote first time synchronization device 100. The time synchronizer 130 causes the information transmitter 160 and the information receiver 170 to transmit and receive PTP frames, such as Sync frames, Delay_Req frames, and Delay_Resp frames, to cause the first time synchronization device 100 to calculate a time difference (step S305). Therefore, if the calculated time difference is greater than 30 seconds, which is an example of the threshold value, the time synchronizer 130 in the first time synchronization device 100 performs time synchronization to synchronize the time with the second time synchronization device 200, which is the current GM.After the time difference is calculated, the GM selector 120 selects the first time synchronization device 100, which is the new time synchronization device, as the new GM. The GM selector 120 then notifies the first time synchronization device 100 that it is connected to the network 500 as the new GM (step S306), transmits a PTP frame transmission restart message to the second time synchronization device 200, which is the current GM (step S307), and terminates the GM selection process upon reconnection.

[0054] As described above, in the time synchronization system 1 according to the present embodiment, the GM selector 120 in each of the time synchronization devices 100 to 400 on the network 500 performs the GM selection process at system startup as an example of the GM arbitration process to select a GM. If selected as a GM, the time synchronization system as the GM causes the time synchronizer 130 to perform time synchronization. If not selected as a GM, the time synchronization device as the follower device causes the time synchronizer 130 to perform time synchronization. The identity information storage 112 stores identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) for identifying the first time synchronization device 100 selected as the GM.When the first time synchronization device 100 is disconnected and removed from the time synchronization system 1, the GM selector 120 in each of the time synchronization devices 200 to 400 performs the GM removal GM selection process as an example of the GM arbitration process and selects the second time synchronization device 200 as the new GM. When a new time synchronization device is connected to the time synchronization system 1 and the GM selector 120 identifies the new time synchronization device as the removed first time synchronization device 100 based on the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D), the GM selector 120 reselects the first time synchronization device 100 as the GM without performing the GM arbitration process.

[0055] As described above, in the time synchronization system 1 according to the present embodiment, when the new time synchronization device connected to the network 500 is the first time synchronization device 100, which is the returned previous GM, each of the time synchronization devices 200 to 400 selects the first time synchronization device 100 as the GM without performing the GM arbitration process. The first time synchronization device 100 with the highest clock accuracy can then start time synchronization as the GM. The time synchronization system 1 according to the present embodiment can therefore switch to a GM with higher clock accuracy faster than the time synchronization system in which the GM arbitration process is performed to reselect the returned previous GM. This reduces time synchronization abnormalities resulting from the GM arbitration process using the BMCA.

[0056] Specifically, in the time synchronization system 1 according to the present embodiment, the values of the identification information (PrTM_A, PrTM_B, PrTM_C, and PrTM_D) are used to perform the GM arbitration process and indicate the priority level of the first time synchronization device 100. The GM selector 120 in each of the time synchronization devices 200 to 400 does not allow the identification information storage 112 to update the value of the identification information (PrTM_A, PrTM_B, PrTM_C, and PrTM_D) when the GM arbitration process is performed after the first time synchronization device 100 is disconnected from the time synchronization system 1 and the second time synchronization device 200 is selected as a new GM.When a new time synchronization device is connected to the time synchronization system 1 and the priority level contained in the identification information (PrTM_B, PrTM_C or PrTM_D) stored in the identification information memory 112 is equal to the priority level indicated in the identification information acquired from the new time synchronization device, the GM selector 120 selects the new time synchronization device, specifically, the first time synchronization device 100, as the GM.

[0057] In a known time synchronization system, control is performed when the first time synchronization device, which is a GM, is disconnected and removed. As in Fig. As shown in Figure 8, at a first time t1 before the removal of the first time synchronization device, the value of the identification information (PrTM_A, PrTM_B, PrTM_C, or PrTM_D) contained in the announcement frame transmitted and received between the time synchronization devices is 1, i.e., equal to the value of the identification information PrTM_A of the first time synchronization device, or in other words, the value of the priority information PrA. Therefore, PrTM_A = PrTM_B = PrTM_C = PrTM_D = PrA = 1.

[0058] For example, if in the Fig. 8, in the GM arbitration process, an announcement frame containing the identification information PrTM_A is transmitted from a first port, which is a master port, of the first time synchronization device to a second port, which is a device port, of the fourth time synchronization device, the fourth time synchronization device receives the announcement frame, compares the value 4 of the identification information PrTM_D stored in the fourth time synchronization device with the value of the identification information PrTM_A, and updates the value of the identification information PrTM_D to 1.When, in the first domain, an announcement frame containing the identification information PrTM_D with the updated value 1 is transmitted from a first port, which is a master port, of the fourth time synchronization device to a second port, which is a device port, of the third time synchronization device, the third time synchronization device receives the announcement frame, compares the value 3 of the identification information PrTM_C stored in the third time synchronization device with the value of the identification information PrTM_D, and updates the value of the identification information PrTM_C to 1.In the first domain, when an announcement frame containing the identification information PrTM_C with the updated value 1 is transmitted from a first port, which is a master port, of the third time synchronization device to a second port, which is a device port, of the second time synchronization device, the second time synchronization device receives the announcement frame, compares the value 2 of the identification information PrTM_B stored in the second time synchronization device with the value of the identification information PrTM_C, and updates the value of the identification information PrTM_B to 1.The second domain becomes the same as the first domain described above by replacing the second time synchronization device with the fourth time synchronization device, replacing the fourth time synchronization device with the second time synchronization device, replacing the first port with the second port, and replacing the second port with the first port. Therefore, the example with these components is not shown or described in detail to avoid redundancy.

[0059] At a second time t2, at which the first time synchronization device is removed, each time synchronization device connected to the network restarts the selection of a new GM in the GM arbitration process. Each time synchronization device transmits and receives an announcement frame containing the priority information (PrB, PrC, or PrD) of the corresponding time synchronization device to and from adjacent time synchronization devices and repeatedly compares the values of the priority information (PrB, PrC, and PrD) to select the second time synchronization device with the minimum value of 2 as the new GM. Each time synchronization device updates the value of the identification information PrTM_B, PrTM_C, or PrTM_D stored in the corresponding time synchronization device to the value 2, which is equal to the value of the priority information PrB of the second time synchronization device.Therefore, the value of the identification information PrTM_B, PrTM_C and PrTM_D of the respective time synchronization device is PrTM_B = PrTM_C = PrTM_D = PrB = 2.

[0060] At a third time t3, after a new GM is selected, the third time synchronization device and the fourth time synchronization device, as follower devices, perform a time synchronization with the second time synchronization device, which is the new GM. For example, in the Fig. In the first domain shown in Figure 8, time synchronization frames are transmitted and received between the second port, which is the master port, of the second time synchronization device and the first port, which is the device port, of the third time synchronization device, in order to synchronize the time of the third time synchronization device with the time of the second time synchronization device, which is the new GM. In the first domain, time synchronization frames are transmitted and received between the second port, which is the master port, of the third time synchronization device and the first port, which is the device port, of the fourth time synchronization device, in order to synchronize the time of the fourth time synchronization device with the time of the third time synchronization device, which allows the time of the fourth time synchronization device to be synchronized with the time of the second time synchronization device, which is the new GM.The second domain becomes the same as the first domain described above by replacing the third time synchronization device with the fourth time synchronization device, replacing the fourth time synchronization device with the third time synchronization device, replacing the first port with the second port, and replacing the second port with the first port. Therefore, the example with these components is not shown or described in detail to avoid redundancy.

[0061] At a fourth time t4, at which the first time synchronization device returns, each time synchronization device, including the first time synchronization device, initiates a selection of a new GM in the GM arbitration process. Specifically, the first time synchronization device transmits and receives an announcement frame containing the first time synchronization device's identification information PrTM_A to and from adjacent time synchronization devices and repeatedly compares the values of the identification information (PrTM_A, PrTM_B, PrTM_C, and PrTM_D) to select the first time synchronization device with the minimum value of 1 as the new GM.Each time synchronization device updates the value of the identification information PrTM_B, PrTM_C, or PrTM_D stored in the corresponding time synchronization device to the same value as the priority information PrTM_A of the first time synchronization device, in other words, the same as the priority information PrTM_A. Therefore, the value of the identification information PrTM_A, PrTM_B, PrTM_C, or PrTM_D of the respective time synchronization device, including the first time synchronization device, returns to PrTM_A = PrTM_B = PrTM_C = PrTM_D = PrA = 1.

[0062] In the Fig. 8, for example, when an announcement frame containing the identification information PrTM_A is transmitted from the first port, which is the master port, of the first time synchronization device to the second port, which is the master port, of the fourth time synchronization device, the fourth time synchronization device receives the announcement frame, compares the value 2 of the identification information PrTM_D stored in the fourth time synchronization device with the value of the identification information PrTM_A, and updates the value of the identification information PrTM_D to 1. The fourth time synchronization device changes the first port from the device port to the master port and the second port from the master port to the device port.At a fifth time t5 after changing the ports of the fourth time synchronization device, in the first domain, when an announcement frame containing the identification information PrTM_D with the updated value 1 is transmitted from the first port, which is the master port, of the fourth time synchronization device to the second port, which is the master port, of the third time synchronization device, the third time synchronization device receives the announcement frame, compares the value 2 of the identification information PrTM_C stored in the third time synchronization device with the value of the identification information PrTM_D, and updates the value of the identification information PrTM_C to 1. The third time synchronization device changes the first port from the device port to the master port and the second port from the master port to the device port.

[0063] At a sixth time t6, after the ports of the third time synchronization device are changed, in the first domain, when an announcement frame containing the identification information PrTM_C with the updated value 1 is transmitted from the first port, which is the master port, of the third time synchronization device to the second port, which is the master port, of the second time synchronization device, the second time synchronization device receives the announcement frame, compares the value 2 of the identification information PrTM_B stored in the second time synchronization device with the value of the identification information PrTM_C, and updates the value of the identification information PrTM_B to 1. The second time synchronization device changes the first port from the device port to the master port and the second port from the master port to the device port.In a period before the first time synchronization device is selected as a new GM, specifically, in a period between the third time t3 and a seventh time t7 at which the ports of the second time synchronization device are changed, each time synchronization device does not perform time synchronization when a frame for time synchronization is received from an adjacent time synchronization device. The second domain becomes the same as the first domain described above by replacing the second time synchronization device with the fourth time synchronization device, replacing the fourth time synchronization device with the second time synchronization device, replacing the first port with the second port, and replacing the second port with the first port. Therefore, the example of these components will not be shown and described in detail to avoid redundancy.

[0064] In a known time synchronization system, when the first time synchronization device, which is a remote GM, returns, the first time synchronization device may be reselected as a new GM in the GM arbitration process. Therefore, the other time synchronization devices cannot perform time synchronization until the GM switches from the second time synchronization device 200, which is the current GM, to the first time synchronization device 100, which becomes the new GM, potentially causing a time synchronization abnormality.

[0065] As in Fig. As shown in Figure 9, in the time synchronization system 1 according to the present embodiment, each of the time synchronization devices 100 to 400 transmits and receives an announcement frame at an eleventh time point t11 before the first time synchronization device 100 is removed, similar to the time synchronization devices 100 to 400 at time point t1 in the conventional time synchronization system. In the time synchronization system 1 according to the present embodiment, the time synchronization devices 200 to 400 each restart selection of a new GM in the GM arbitration process at a twelfth time point t12 at which the first time synchronization device 100 is removed, similar to the time synchronization devices 200 to 400 at the second time point t2 in the conventional time synchronization system.

[0066] At a thirteenth time point t13, at which the second time synchronization device 200 is selected as the new GM, in the time synchronization system 1 according to the present embodiment, each of the time synchronization devices 200 to 400 does not update the value of the identification information (PrTM_B, PrTM_C, or PrTM_D) stored in the corresponding time synchronization device to the value 2, which is equal to the priority information PrB of the second time synchronization device 200. Therefore, the value of the identification information (PrTM_B, PrTM_C, and PrTM_D) remains PrTM_B = PrTM_C = PrTM_D = PrA = 1.

[0067] At a fourteenth time point t14 at which the time synchronization device 100 returns, in the time synchronization system 1 according to the present embodiment, the first time synchronization device 100 transmits an announcement frame containing the identification information PrTM_A to the adjacent time synchronization devices, and the other time synchronization devices 200 to 400 each confirm that the value of the identification information (PrTM_B, PrTM_C, or PrTM_D) stored in the corresponding time synchronization device 200 to 400 is equal to the value of the identification information PrTM_A contained in the received announcement frame. The time synchronization device 100 is therefore reselected as the new GM.

[0068] If in a Fig.For example, in the first domain D1 shown in Figure 9, when an announcement frame containing the identification information PrTM_A is transmitted from the first port, which is a master port, of the first time synchronization device 100 to the second port, which is the master port, of the fourth time synchronization device 400 in the GM arbitration process, the fourth time synchronization device 400 receives the announcement frame, compares the value 1 of the identification information PrTM_D stored in the fourth time synchronization device 400 with the value of the identification information PrTM_A, and determines that the values are equal.If, in the first domain D1, the time difference between the time of the first time synchronization device 100 and the time of the second time synchronization device 200, which is the current GM, is less than or equal to 30 seconds, which is an example of the threshold, the fourth time synchronization device 400 determines at a fifteenth time point that the first time synchronization device 100 is the removed previous GM, and notifies the first time synchronization device 100 that it is connected to the network 500 as the new GM, and transmits a PTP frame transmission restart message to the second time synchronization device 200. At a sixteenth time point in the first domain D1, the time synchronization devices 100 to 400 are each in the same state as at the eleventh time point t11, and the first time synchronization device 100 returns to the network 500 and performs time synchronization as the new GM through.The second domain D2 becomes the same as the first domain D1 described above by replacing the second time synchronization device with the fourth time synchronization device, replacing the fourth time synchronization device with the second time synchronization device, replacing the first port with the second port, and replacing the second port with the first port. Therefore, the example with these components is not shown or described in detail to avoid redundancy.

[0069] In the time synchronization system 1 according to the present embodiment, when the first time synchronization device 100, which is the removed GM, returns, the first time synchronization device 100 is reselected as the new GM without the GM arbitration process. Therefore, the time synchronization system 1 according to the present embodiment allows the other time synchronization devices 300 and 400 to perform time synchronization with the second time synchronization device 200 before switching the GM from the second time synchronization device 200, which is the current GM, to the first time synchronization device 100, which is the new GM. Therefore, the time synchronization system 1 according to the present embodiment can reduce time synchronization abnormalities more than a conventional time synchronization system.

[0070] In the time synchronization system 1 according to the present embodiment, when a new time synchronization device is connected to the time synchronization system 1, the time synchronization devices 200 to 400 each cause the time difference calculator 140 to compare the time of the second time synchronization device 200, which is the current GM, with the time of the new time synchronization device to calculate a time difference.

[0071] As described above, in the time synchronization system 1 according to the present embodiment, the time synchronization devices 200 to 400 can determine the time difference between the time of the second time synchronization device 200, which is the current GM, and the time of the new time synchronization device.

[0072] Specifically, in the time synchronization system 1 according to the present embodiment, when the new time synchronization device is the remote first time synchronization device 100 and the calculated time difference is less than or equal to 30 seconds, which is an example of the predetermined threshold, the new time synchronization device performs time synchronization as the new GM without performing time synchronization with the second time synchronization device 200, which is the current GM. Therefore, when the new time synchronization device is the remote first time synchronization device 100, the time synchronization devices 200 to 400, as follower devices, each cause the time synchronizer 130 to perform time synchronization with the new time synchronization device, in other words, with the first time synchronization device 100, which has not performed time synchronization after being connected to the time synchronization system 1.

[0073] As described above, in the time synchronization system 1 according to the present embodiment, when the time difference between the time of the first time synchronization device 100 and the time of the second time synchronization device 200, which is the current GM, is smaller than the threshold, the first time synchronization device 100 can start time synchronization as a new GM without performing time synchronization with the current GM. Therefore, the time period before a new GM starts performing time synchronization in the time synchronization system 1 according to the present embodiment is shorter than in a time synchronization system that synchronizes the time of the current GM with the time of the new GM regardless of the time difference.

[0074] In the time synchronization system 1 according to the present embodiment, if the new time synchronization device is the remote first time synchronization device 100 and the calculated time difference is greater than 30 seconds, which is an example of the predetermined threshold, the new time synchronization device performs time synchronization as the new GM after performing time synchronization with the second time synchronization device 200, which is the current GM. Therefore, if the new time synchronization device is the remote first time synchronization device 100, the time synchronization devices 200 to 400, as follower devices, each cause the time synchronizer 130 to perform time synchronization with the new time synchronization device, in other words, with the first time synchronization device 100 that has performed time synchronization after being connected to the time synchronization system 1.

[0075] As described above, in the time synchronization system 1 according to the present embodiment, when the time difference between the time of the first time synchronization device 100 and the time of the second time synchronization device 200, which is the current GM, is greater than the threshold, the first time synchronization device 100 can start time synchronization as a new GM after synchronizing the time with the second time synchronization device 200. Therefore, the time synchronization system 1 according to the present embodiment can reduce time synchronization abnormalities more than a time synchronization system that does not synchronize the time of the current GM with the time of the new GM when the time difference is greater than the threshold.

[0076] In the time synchronization system 1 according to the present embodiment, when a new time synchronization device is connected to the time synchronization system 1 and the priority level indicated in the identification information (PrTM_B, PrTM_C, or PrTM_D) stored in the identification information memory 112 is greater than the priority level indicated in the identification information acquired from the new time synchronization device, the GM selector 120 in each of the time synchronization devices 200 to 400 does not select a new GM. In this case, the new time synchronization device, which is not the removed first time synchronization device 100, is allowed to transmit and receive information to and from the time synchronization devices (200 to 400) after performing time synchronization with the second time synchronization device 200, which is the current GM.

[0077] As described above, in the time synchronization system 1 according to the present embodiment, the new time synchronization device can start transmitting and receiving information as a new follower device to and from the other time synchronization devices after synchronizing the time of the new time synchronization device with the time of the second time synchronization device 200, which is the current GM. Therefore, the time synchronization system 1 according to the present embodiment can reduce time synchronization abnormalities more than a time synchronization system in which a new time synchronization device starts transmitting and receiving information to and from the other time synchronization devices without synchronizing the time of the current GM with the time of the new time synchronization device, which is a follower device.

[0078] In the time synchronization system 1 according to the present embodiment, when a new time synchronization device is connected to the time synchronization system 1 and the priority level indicated in the identification information (PrTM_B, PrTM_C, or PrTM_D) stored in the identification information memory 112 is lower than the priority level indicated in the identification information acquired from the new time synchronization device, the GM selector 120 in each of the time synchronization devices 200 to 400 does not select a new GM. In this case, the new time synchronization device is disconnected from the time synchronization system 1.

[0079] As described above, in the time synchronization system 1 according to the present embodiment, the new time synchronization device other than the removed first time synchronization device 100 performs time synchronization as a new GM, thereby preventing time synchronization abnormalities. Modifications

[0080] In the present embodiment, the value of the identification information PrTM_A, PrTM_B, PrTM_C, or PrTM_D is 1, which is the value of the priority information PrA of the first time synchronization device 100 selected as the GM, or in other words, the value indicating the priority level of the first time synchronization device 100. However, the value may be any value for identifying the first time synchronization device 100. For example, the value of the identification information PrTM_A, PrTM_B, PrTM_C, or PrTM_D may be a value indicating the station number, a value indicating the IP address, or a value indicating the clock ID of the first time synchronization device 100 selected as the GM.

[0081] As in the present embodiment, when the time difference between the time of the first time synchronization device 100, which is the returned previous GM, and the time of the second time synchronization device 200, which is the current GM, is smaller than the threshold, the first time synchronization device 100 can start time synchronization as the new GM without performing time synchronization with the current GM. However, the first time synchronization device 100 can start time synchronization after performing time synchronization with the current GM regardless of the time difference.

[0082] As in the present embodiment, when the priority level indicated in the identification information (PrTM_B, PrTM_C, or PrTM_D) stored in the corresponding time synchronization device is lower than the priority level indicated in the identification information acquired from the new time synchronization device connected to the time synchronization system 1, the time synchronization devices 200 to 400 may each perform control of not selecting a new GM. However, the time synchronization devices 200 to 400 may perform the GM arbitration process using the BMCA to select a new GM.

[0083] In this case, if the priority level of the new time synchronization device is higher than the priority level of the second time synchronization device 200, which is the current GM, the new time synchronization device is selected as the new GM. If the new time synchronization device is selected as the new GM, such as when the first time synchronization device 100, which is the returned previous GM, is reselected as the new GM, and the time difference between the time of the new time synchronization device and the time of the second time synchronization device 200, which is the current GM, is greater than the threshold, the new time synchronization device can start time synchronization as the new GM after synchronizing the time with the second time synchronization device 200.

[0084] In this case, if the priority level of the new time synchronization device is lower than the priority level of the second time synchronization device 200, which is the current GM, the new time synchronization device becomes a new follower device instead of being selected as the new GM. When the new time synchronization device becomes a new follower device, as in the present embodiment, the new time synchronization device can be allowed to transmit and receive information to and from the time synchronization devices (200 to 400) after performing time synchronization with the second time synchronization device 200, which is the current GM.

[0085] The main operating sections of the first time synchronization device 100, the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400, each including the controller 51, the main memory 52, the external memory 53, the operation device 54, the display 55, and the transceiver 56, which are connected to each other by the internal bus 50, may be implemented by a general computer system instead of a dedicated system.For example, a computer program for performing the above operation may be stored in a non-transitory computer-readable recording medium such as a flash memory or a digital versatile disk read-only memory (DVD-ROM), distributed, and installed in a computer to implement the first time synchronization device 100, the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400 that perform the above processes. The computer program may be stored in a storage device in a server on a communication network such as the Internet and downloaded to a general computer system to implement the first time synchronization device 100, the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400.

[0086] When the functions of the first time synchronization device 100, the second time synchronization device 200, the third time synchronization device 300, and the fourth time synchronization device 400 are implemented partly by an operating system (OS) and partly by an application program, or by cooperation between the operating system and the application program, only the portions of the application program may be stored in a non-volatile recording medium or a storage device.

[0087] Furthermore, the computer program can be superimposed on a carrier wave to be delivered to a communications network. For example, the computer program can be posted on a bulletin board system on a communications network to be delivered through the network. The above processes can be performed by starting the computer program and executing the computer program under the control of the operating system in the same way as in any other application program.

[0088] The above describes some exemplary embodiments for illustrative purposes. Although the foregoing discussion has presented specific embodiments, it will be understood by those skilled in the art that changes may be made in form and detail without departing from the broader spirit and scope of the invention. Accordingly, the description and drawings are to be regarded as exemplary rather than restrictive. This detailed description, therefore, is not to be taken in a limiting sense, and the scope of the invention is defined solely by the appended claims, along with the full scope of equivalents capable of being attributed to such claims. List of reference symbols 1 time synchronization system 50 internal bus 51 Control 52 main memory 53 external storage 54 Control unit 55 Advertisement 56 transceivers 59 Control program 100 first time synchronization device 110 Information Storage 111 Priority Information Memory 112 Identification information memory 113 Arbitration Priority Information Memory 120 GM selectors 130 time synchronizers 140 time difference calculators 150 Network connection control 160 information transmitters 170 information recipients 200 second time synchronization device 300 third time synchronization device 400 fourth time synchronization device 500 Network QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions. Cited patent literature

[0000] JP 2018 - 037 885

[0006] WO 2020 / 059 139

[0006]

Claims

[1] A time synchronization device for performing time synchronization as a grandmaster or as a follower device in a time synchronization system, the time synchronization device comprising: a grandmaster selector that selects the grandmaster by performing a grandmaster arbitration process to identify a time synchronization device corresponding to the grandmaster from a plurality of time synchronization devices included in the time synchronization system; a time synchronizer which performs time synchronization as the grandmaster when the time synchronization device is selected as the grandmaster, and which performs time synchronization as the follower device when the time synchronization device is not selected as the grandmaster; and an identification information memory which stores identification information for identifying the one time synchronization device selected as the Grandmaster, wherein, when the one time synchronization device is disconnected and removed from the time synchronization system, the grandmaster selector selects the grandmaster from the plurality of time synchronization devices not including the one time synchronization device by performing the grandmaster arbitration process, and wherein, when a new time synchronization device is connected to the time synchronization system and the grandmaster selector identifies the new time synchronization device as the removed one time synchronization device based on the identification information, the grandmaster selector selects the new time synchronization device as the grandmaster without performing the grandmaster arbitration process. [2] Time synchronization device according to claim 1, wherein the identification information is used to perform the Grandmaster arbitration process and indicates a priority level of one time synchronization device, the identification information memory does not update the identification information when the one time synchronization device is removed from the time synchronization system and the grandmaster is selected in the grandmaster arbitration process from the plurality of time synchronization devices which do not include the one time synchronization device, and, when a new time synchronization device is connected to the time synchronization system and a priority level indicated in the identification information stored in the identification information memory is equal to a priority level indicated in the identification information acquired from the new time synchronization device, the grandmaster selector selects the new time synchronization device as the grandmaster. [3] Time synchronization device according to claim 1 or 2, further comprising: a time difference calculator which, when a new time synchronization device is connected to the time synchronization system, compares a time of a current grandmaster with a time of the new time synchronization device to calculate a time difference. [4] Time synchronization device according to claim 3, wherein, if the new time synchronization device is the remote one time synchronization device and the calculated time difference is less than or equal to a predetermined threshold, the new time synchronization device performs time synchronization as a new grandmaster without performing time synchronization with the current grandmaster, and, if the new time synchronization device is the remote one time synchronization device, the time synchronizer in the time synchronization device that is the follower device performs time synchronization with the new time synchronization device that has not performed time synchronization after being connected to the time synchronization system. [5] Time synchronization device according to claim 3, wherein, if the new time synchronization device is the remote one time synchronization device and the calculated time difference is greater than a predetermined threshold, the new time synchronization device performs time synchronization as a new grandmaster after performing time synchronization with the current grandmaster, and, if the new time synchronization device is the remote one time synchronization device, the time synchronizer in the time synchronization device that is the follower device performs time synchronization with the new time synchronization device that has performed time synchronization after being connected to the time synchronization system. [6] Time synchronization device according to claim 2, wherein the Grandmaster selector does not select a new Grandmaster if the priority level specified in the identification information stored in the identification information memory is different from the priority level specified in the identification information obtained from the new time synchronization device, and, if the priority level indicated in the identification information stored in the new time synchronization device is lower than a priority level indicated in the identification information stored in another time synchronization device included in the time synchronization system, the new time synchronization device is enabled, after performing time synchronization with the grandmaster, to transmit information to and receive information from the other time synchronization device. [7] Time synchronization device according to claim 2, wherein the Grandmaster selector does not select a new Grandmaster if the priority level specified in the identification information stored in the identification information memory is different from the priority level specified in the identification information obtained from the new time synchronization device, and, if the priority level indicated in the identification information stored in the new time synchronization device is higher than a priority level indicated in the identification information stored in another time synchronization device included in the time synchronization system, the new time synchronization device is disconnected from the time synchronization system. [8] Time synchronization system comprising: several time synchronization devices, each of which performs time synchronization as a grandmaster or as a follower device, wherein a time synchronization device of the plurality of time synchronization devices comprises: a grandmaster selector that selects the grandmaster by performing a grandmaster arbitration process to identify a time synchronization device corresponding to the grandmaster from the plurality of time synchronization devices, a time synchronizer which performs time synchronization as the grandmaster when the time synchronization device is selected as the grandmaster, and which performs time synchronization as the follower device when the time synchronization device is not selected as the grandmaster, and an identification information memory which stores identification information for identifying the one time synchronization device selected as the Grandmaster, wherein, when the one time synchronization device is disconnected and removed from the time synchronization system, the grandmaster selector selects the grandmaster from the plurality of time synchronization devices not including the one time synchronization device by performing the grandmaster arbitration process, and wherein, when a new time synchronization device is connected to the time synchronization system and the grandmaster selector identifies the new time synchronization device as the removed one time synchronization device based on the identification information, the grandmaster selector selects the new time synchronization device as the grandmaster without performing the grandmaster arbitration process. [9] Time synchronization method, comprising: Selecting, with a computer, a grandmaster of a time synchronization system by performing a grandmaster arbitration process to identify a computer corresponding to the grandmaster from a plurality of computers included in the time synchronization system; Performing, with the computer, a time synchronization as the grandmaster when the computer is selected as the grandmaster, and performing a time synchronization as a follower device of the time synchronization system when the computer is not selected as the grandmaster; and Storing, with the computer, identification information for identifying the computer selected as the Grandmaster, where selecting the Grandmaster includes: Selecting, when the one computer is disconnected and removed from the time synchronization system, the grandmaster from the plurality of computers not including the one computer by performing the grandmaster arbitration process, and When a new computer is connected to the time synchronization system and the new computer is identified as the remote one based on the identification information, selecting the new computer as the grandmaster without performing the grandmaster arbitration process. [10] Program for causing a computer to function as: a grandmaster selector that selects a grandmaster of a time synchronization system by performing a grandmaster arbitration process to identify a computer corresponding to the grandmaster of the time synchronization system from a plurality of computers included in the time synchronization system; a time synchronizer which performs time synchronization as the grandmaster when the computer is selected as the grandmaster, and which performs time synchronization as a follower device of the time synchronization system when the computer is not selected as the grandmaster; and an identification information memory which stores identification information for identifying the one computer selected as the Grandmaster, wherein, when the one computer is disconnected and removed from the time synchronization system, the grandmaster selector selects the grandmaster from the plurality of computers not including the one computer by performing the grandmaster arbitration process, and wherein, when a new computer is connected to the time synchronization system and the grandmaster selector identifies the new computer as the remote one based on the identification information, the grandmaster selector selects the new computer as the grandmaster without performing the grandmaster arbitration process.

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