Communication station, communication system, time synchronization method, and time synchronization program

Abstract

A communication station (10) comprises a time estimation unit (120) and a communication unit (110). The time estimation unit (120) estimates an estimated time from a reference time received from a grand master station that is the transmission source of the reference time. When the reference time received from the grand master station is interrupted, the communication unit (110) serves as a new grand master station and transmits, as the reference time to another communication station, the estimated time continuously estimated by the time estimation unit (120). The communication station (10) receives the reference time directly from the grand master station or receives the reference time from the grand master station via another communication station.

Description

Communication Station, Communication System, Time Synchronization Method, and Time Synchronization Program

[0001] The present disclosure relates to a communication station, a communication system, a time synchronization method, and a time synchronization program. In particular, it relates to a time synchronization method in a communication system in which a plurality of communication stations perform time synchronization via a communication protocol for time synchronization.

[0002] In the time synchronization communication protocol IEEE802.1AS, one grandmaster station that distributes the internal time of its own communication station as a reference time is selected in the network. Hereinafter, the grandmaster station may be referred to as a GM station. Thereafter, a time receiver station that has received the reference time distributed by the GM station derives an estimated time obtained by estimating the internal time of the GM station at the time of reception. This achieves time synchronization for all communication stations belonging to the network. Hereinafter, the time receiver station may be referred to as a TR station. In addition, in IEEE802.1AS, in order to realize redundancy of the GM station, when communication with the selected GM station cannot be established, a new GM station is selected. Thereby, switching of the GM station is performed. However, in the above time synchronization communication protocol, there is no mention that the GM station after switching inherits the reference time of the GM station before switching when the GM station is switched. Therefore, the TR station will have a time offset if a reference time that is discontinuous with the internal time of the GM station before switching is distributed from the GM station after switching.

[0003] Patent Document 1 discloses a method in which a BC device arranged directly under a plurality of GM stations inherits the reference time of the GM station before switching and distributes the reference time in order to avoid time offset. BC is an abbreviation for Boundary Clock.

[0004] International Publication No. 2022 / 259381

[0005] In the technology of Patent Document 1, the BC device aggregates the distribution paths of reference time between the master device and the slave devices. Therefore, if the BC device fails, the reference time cannot be distributed, which leads to the problem of low redundancy.

[0006] An object of the present disclosure is to provide a communication system with high redundancy and no time offset.

[0007] The communication station relating to this disclosure includes a time estimation unit that estimates an estimated time from the reference time received from a grandmaster station which is the source of the reference time, and a communication unit that, when the reference time received from the grandmaster station is interrupted, becomes a new grandmaster station and transmits the estimated time, which has been continuously estimated by the time estimation unit, to other communication stations as the reference time.

[0008] According to the communications bureau described herein, it is possible to provide a highly redundant and time-delay-free communications system.

[0009] A diagram showing an example of the functional configuration of a communication station according to Embodiment 1. A diagram showing an example of the hardware configuration of a communication station according to Embodiment 1. A sequence diagram showing an example of communication in the communication system according to Embodiment 1. A flowchart showing an example of the operation of a communication station according to Embodiment 1. A table showing the determination conditions of the post-GM station and the information to be set in the reference time information in the communication station according to Embodiment 1. A diagram showing a comparative example for comparison with the operation example of a communication station according to Embodiment 1. A diagram showing an example of the operation of a communication station according to Embodiment 1. A diagram showing an example where the communication station according to Embodiment 1 does not inherit the clock ratio. A diagram showing the case where communication delay is considered in the operation example of a communication station according to Embodiment 1. A diagram showing an example of the hardware configuration of a communication station according to a modified version of Embodiment 1.

[0010] The following description of this embodiment will be illustrated with reference to the figures. In each figure, identical or corresponding parts are denoted by the same reference numerals. In the description of the embodiment, descriptions of identical or corresponding parts will be omitted or simplified as appropriate. The arrows in the figures mainly indicate the flow of data or processing. In addition, in the description of the embodiment, directions or positions such as up, down, left, right, front, back, front, and back may be indicated. These notations are for the convenience of explanation and do not limit the arrangement, direction, and orientation of the devices, instruments, or parts.

[0011] Embodiment 1.

[0012] ***Description of Configuration*** Figure 1 is a diagram showing an example of the functional configuration of the communication station 10 according to this embodiment. Figure 2 is a diagram showing an example of the hardware configuration of the communication station 10 according to this embodiment. Using Figures 1 and 2, the functional configuration examples and hardware configuration examples of the communication system 500 and communication station 10 according to this embodiment will be explained.

[0013] The communication system 500 comprises multiple communication stations 10 connected by a network 400 and communicating using a time synchronization communication protocol. The multiple communication stations 10 include a GM station selected as the reference for time synchronization.

[0014] The communication station 10 is a computer. The communication station 10 includes a processor 910, as well as other hardware such as memory 921, auxiliary storage device 922, input / output interface 930, and communication interface 950. The processor 910 is connected to the other hardware via signal lines 80 and controls this other hardware.

[0015] The communication station 10 includes, as functional elements, a communication unit 110, a time estimation unit 120, an estimated time counter 130, and an internal time counter 140. In this embodiment, the functions of the communication unit 110 and the time estimation unit 120 are described as being implemented by software. The function of the estimated time counter 130 may be implemented by software or by hardware. Similarly, the function of the internal time counter 140 may be implemented by software or by hardware.

[0016] The processor 910 is a device that executes a time synchronization program. The time synchronization program is a program that realizes the functions of the communication station 10. The processor 910 is an IC that performs arithmetic processing. Specific examples of the processor 910 are a CPU, DSP, and GPU. IC is an abbreviation for Integrated Circuit. CPU is an abbreviation for Central Processing Unit. DSP is an abbreviation for Digital Signal Processor. GPU is an abbreviation for Graphics Processing Unit.

[0017] Memory 921 is a storage device that temporarily stores data. Specific examples of memory 921 include SRAM or DRAM. SRAM is an abbreviation for Static Random Access Memory. DRAM is an abbreviation for Dynamic Random Access Memory. Auxiliary storage device 922 is a storage device that stores data. Specific examples of auxiliary storage device 922 include HDD. Alternatively, auxiliary storage device 922 may be a portable storage medium such as an SD® memory card, CF, NAND flash, flexible disk, optical disk, compact disk, Blu-ray® disc, or DVD. HDD is an abbreviation for Hard Disk Drive. SD® is an abbreviation for Secure Digital. CF is an abbreviation for CompactFlash (registered trademark). DVD is an abbreviation for Digital Versatile Disk.

[0018] The input / output interface 930 is an interface for connecting input / output devices. Specific examples of the input / output interface 930 include USB and HDMI® ports. USB stands for Universal Serial Bus. HDMI® stands for High-Definition Multimedia Interface.

[0019] The communication interface 950 is an interface for communicating with external devices. Specific examples of the communication interface 950 include an Ethernet® port or a wireless communication device.

[0020] The time synchronization program is executed at the communication station 10. The time synchronization program is loaded into the processor 910 and executed by the processor 910. Memory 921 stores not only the time synchronization program but also the OS. OS is an abbreviation for Operating System. The processor 910 executes the time synchronization program while executing the OS. The time synchronization program and the OS may also be stored in auxiliary storage device 922. The time synchronization program and OS stored in auxiliary storage device 922 are loaded into memory 921 and executed by the processor 910. Note that part or all of the time synchronization program may be incorporated into the OS.

[0021] The communications station 10 may have multiple processors that replace the processor 910. These multiple processors share the task of executing the time synchronization program. Each processor is a device that executes the time synchronization program, just like the processor 910.

[0022] Data, information, signal values, and variable values ​​used, processed, or output by the time synchronization program are stored in memory 921, auxiliary storage device 922, or registers or cache memory within the processor 910.

[0023] The word "part" in each section of the communication station 10 may be read as "circuit," "process," "procedure," "process," or "circuitry." The time synchronization program causes the computer to execute each process of the communication station 10, with "part" replaced by "process." The word "process" in each process of the communication station 10 may be read as "program," "program product," "computer-readable storage medium storing the program," or "computer-readable recording medium recording the program." The time synchronization method is performed by the communication station 10 executing the time synchronization program. The time synchronization program may be provided stored on a computer-readable recording medium. The time synchronization program may also be provided as a program product.

[0024] ***Explanation of Operation*** The operation of the communication station 10 according to this embodiment will now be explained. The operation procedure of the communication station 10 corresponds to the time synchronization method. Furthermore, the program that realizes the operation of the communication station 10 corresponds to the time synchronization program.

[0025] Figure 3 is a sequence diagram showing an example of communication in the communication system 500 according to this embodiment. First, the functional overview of the components of the communication station 10 will be explained. In this embodiment, the communication station that is the GM station at the start of communication in the communication system 500 is referred to as the pre-GM station 101. Furthermore, the communication station selected as the GM station after the pre-GM station 101 has left the communication system 500 is referred to as the post-GM station 102. The pre-GM station 101 leaving the communication system 500 means that the pre-GM station 101 is unable to communicate.

[0026] The communication unit 110 is a module that converts communications between communication stations into signals to be exchanged over the network 400 and transmits and receives them. The communication unit 110 also identifies its own communication station as a GM station based on the priority of other communication stations. The communication unit 110 also extracts the parameters necessary for time estimation using the internal time, which is the value of the internal time counter 140, and passes them to the time estimation unit 120. In this embodiment, the communication unit 110 determines whether its own communication station is a later GM station 102. If the communication unit 110 determines that its own communication station is a later GM station 102, it transmits reference time information 50, which includes the estimated time estimated as the internal time of the previous GM station 101 as the reference time 51 of the communication system 500, to the other communication station. When the communication unit 110 receives the reference time information 50, it sets the reference time 51 included in the reference time information 50 to the estimated time counter 130. More specifically, when the communications unit 110 determines that its own communications station is the next GM station 102, it transmits reference time information 50 to the other communications station, which includes the estimated time 31, which is the value of the estimated time counter 130, and the next clock ratio, which is the clock ratio between the previous GM station 101 and the communications station itself.

[0027] The time estimation unit 120 uses parameters passed from the communication unit 110 to estimate the estimated time based on the internal time of the previous GM station 101. The time estimation unit 120 then corrects the estimated time, which is the value of the estimated time counter 130. In this embodiment, the time estimation unit 120 counts the value of the estimated time counter 130, which has been estimated as the internal time of the previous GM station 101, as the estimated time 31. More specifically, when the communication unit 110 receives the reference time information 50, it extracts the reference time 51 included in the reference time information 50 and the previous clock ratio, which is the clock ratio of the previous GM station 101 to the adjacent station, and passes them to the time estimation unit 120. The time estimation unit 120 uses the reference time 51, the previous clock ratio, and the internal time 41 of its own communication station to calculate the clock ratio of the previous GM station 101 and its own communication station as the next clock ratio. The time estimation unit 120 then counts the value of the estimated time counter 130 as the estimated time 31 based on the later clock ratio.

[0028] Here, we will explain the front clock ratio and the rear clock ratio. The front clock ratio is the clock ratio between the adjacent station and the previous GM station 101. The rear clock ratio is the clock ratio between the local station and the previous GM station 101. Therefore, even when transmitting the same clock ratio, the transmitting station transmits the rear clock ratio, which is the clock ratio between the local station and the previous GM station 101, and the receiving station receives the front clock ratio, which is the clock ratio of the adjacent station (i.e., the transmitting station).

[0029] In this manner, the time estimation unit 120 estimates the estimated time using the parameters received from the communication unit 110 and corrects the estimated time, which is the value of the estimated time counter 130. If the estimated time counter 130 is frequency adjustable, the frequency is adjusted according to the clock ratio. If the estimated time counter 130 is not frequency adjustable, the counter value is corrected according to the clock ratio.

[0030] The estimated time counter 130 is a counter that shows the estimated time synchronized between each communication station. The later GM station 102, described later, uses the estimated time 31, which is the value of the estimated time counter 130, to inherit the reference time 51 based on the internal time of the earlier GM station 101.

[0031] The internal time counter 140 is a counter synchronized with the internal clock that indicates the internal time. The internal time, which is the value of the internal time counter 140, cannot be changed from the outside. The internal time, which is the value of the internal time counter 140, is also used to calculate the parameters necessary for time estimation.

[0032] The communication system 500 comprises a plurality of communication stations 10, each utilizing a communication protocol for time synchronization. Each of the plurality of communication stations 10 is assigned a priority level by the time synchronization communication protocol. The plurality of communication stations 10 includes a GM station that serves as the reference for time synchronization. Specifically, the time synchronization communication protocol is IEEE 802.1AS.

[0033] IEEE 802.1AS achieves time synchronization by combining three types of communication functions, mainly shown in Figure 3 (1) to (3). Each communication is performed periodically. (1) Transmitting a detection request signal from an adjacent station: Communication station 10 detects an adjacent station, i.e., a communication station directly connected by cable without going through other communication stations. Each communication station periodically transmits a detection request signal to the adjacent station from all ports and stores the transmission time of the detection request signal. Subsequently, when a detection response signal (storing the reception time of the detection request signal and the transmission time of the detection response signal) is received from the adjacent station, the communication station detects the adjacent station based on the detection response signal and stores the reception time of the detection response signal. At this time, the "communication delay between adjacent stations" is calculated by taking the average of the communication time taken for the round trip. In addition, the "clock ratio with the adjacent station" is calculated based on the local communication station from the ratio of the interval between the transmission time and the interval between the reception time that elapsed between the two detection response signals. (2) Transmission of GM station selection signal Each communication station transmits a GM station selection signal, including its own priority, to all stations in the network 400 from all ports. If no station receives a higher priority than its own between the current transmission and the previous transmission, it determines that it is the GM station 100. (3) Distribution of reference time information 50 The GM station 100 distributes reference time information 50 from all ports, which contains the "reference time," the "communication delay from the GM station to the adjacent station," and the "clock ratio of the GM station relative to the adjacent station." In this embodiment, the estimated time estimated as the internal time of the previous GM station 101 is referred to as the "reference time." In the following, the "communication delay from the GM station to the adjacent station" may be simply referred to as the "communication delay to the adjacent station." Also, the "clock ratio of the GM station relative to the adjacent station" may be simply referred to as the "clock ratio to the adjacent station." In this embodiment, the previous clock ratio, which is the clock ratio between the previous GM station and the adjacent station, is referred to as the "clock ratio to the adjacent station."

[0034] The TR station estimates the internal time of the GM station based on the received reference time information 50. Furthermore, TR stations with multiple ports calculate the new "communication delay to adjacent stations" and "clock ratio to adjacent stations" from the TR station that received the information from the GM station using the following formula, and transmit it as new reference time information 50 from the port that has not received it. Communication delay to adjacent stations (new) = Communication delay to adjacent stations (old: received value) + Communication delay between adjacent stations Clock ratio to adjacent stations (new) = (1 + Clock ratio to adjacent stations (old: received value)) × (1 + Clock ratio with adjacent station) - 1

[0035] The internal time of the GM station is estimated by the TR station using the following formula (Equation 1). Hereafter, the estimated internal time of the GM station will be referred to as the estimated time. The estimated time is calculated each time the internal time of the TR station is updated, not limited to the reception timing in (3).

[0036] (Formula 1) Estimated time = Reference time + Communication delay to adjacent station + Communication delay between adjacent stations + (Current internal time of TR station - Internal time of TR station at the time of reference time reception) × (1 + Clock ratio to adjacent station) × (1 + Clock ratio with adjacent station)

[0037] Here, {(1 + clock ratio to adjacent station) × (1 + clock ratio with adjacent station) - 1} corresponds to the "clock ratio with GM station". Of the variables used in (Equation 1), "communication delay to adjacent station" and "clock ratio to adjacent station" change when the GM station is changed.

[0038] Figure 4 is a flowchart showing an example of the operation of the communication station 10 according to this embodiment. In step S101, the communication unit 110 periodically transmits a (2) GM station selection signal for selecting a GM station in the communication system 500.

[0039] In step S102, the communications unit 110 determines whether it has received a (2) GM station selection signal with a higher priority than its own station during the two transmissions of the (2) GM station selection signal. If it has received a (2) GM station selection signal with a higher priority than its own station, the communications unit is recognized as a TR station, and the transmission of (3) reference time information 50 communication is limited to when the (3) reference time information 50 communication is received (step S102a), and the process returns to step S101. If it has not received a (2) GM station selection signal with a higher priority than its own station, the communications unit is recognized as a GM station, and the process proceeds to step S103.

[0040] In step S103, the communications unit 110 determines whether it has previously received a (2) GM station selection signal that had a higher priority than its own station. If it has previously received a (2) GM station selection signal that had a higher priority than its own station, it recognizes itself as the next GM station 102, and the process proceeds to step S104. If it has not previously received a (2) GM station selection signal that had a higher priority than its own station, it recognizes itself as the previous GM station 101, and the process proceeds to step S105.

[0041] In step S104, the communication unit 110 recognizes its own communication station as the next GM station 102. Thereafter, the communication unit 110 periodically transmits (3) reference time information 50 which stores the following variables: Reference time: Estimated time 31, which is the value of the estimated time counter 130; Clock ratio with GM station: Next clock ratio, which is the clock ratio with the previous GM station; After that, the process returns to step S101.

[0042] In step S105, the communication unit 110 recognizes its own communication station as the previous GM station 101. Thereafter, the communication unit 110 periodically transmits (3) reference time information 50 communication containing the following variables: Reference time: Internal time 41, which is the value of the internal time counter 140; Clock ratio with GM station: 0; After that, the process returns to step S101.

[0043] Fig. 5 is a table showing post-GM station determination conditions and information set in reference time information 50 in the communication station 10 according to the present embodiment. The communication unit 110 of each communication station performs communications (1) to (3) as shown in the sequence diagram of Fig. 3. (2) Each time communication for GM station selection is performed, it determines whether the local communication station is a GM station or a TR station. When the local communication station is a GM station, the communication unit 110 determines whether the local communication station is a previous GM station or a post GM station based on the post-GM station determination conditions in Fig. 5. Thereafter, the communication unit 110 transmits the communication of (3) storing the content of the corresponding reference time information in Fig. 5. On the other hand, when the local communication station is a TR station, the communication unit 110 uses an internal time counter 140 to extract parameters required for time estimation and passes them to the time estimation unit 120. The time estimation unit 120 uses the parameters received from the communication unit 110 to calculate an estimated time 31 according to the above (Formula 1), and writes the estimated time 31 into the estimated time counter 130.

[0044] Here, the time synchronization process in the communication station 10 described with reference to Fig. 4 is rephrased as follows. After GM station switching, the post GM station 102, which is the switched GM station, distributes the estimated time of the previous GM station 101 as "reference time 51". Specifically, the post GM station 102 was a TR station until immediately before GM switching, and calculates the estimated time 31 based on the reference time of the previous GM station 101 using (Formula 1). Therefore, this calculation is continued even after GM switching, and the calculated estimated time 31 is used as the "reference time 51". In addition, to allow other TR stations to continue estimating the internal time of the previous GM station 101, the post GM station 102 does not set the clock ratio with the GM station stored in (3) reference time information 50 to 0, but inherits it as the clock ratio with the previous GM station. The post GM station stores the value of the estimated time counter and the clock ratio with the previous GM station in (3) reference time information 50 and distributes them periodically.

[0045] The operation of the communication station 10 according to the present embodiment will be specifically described with reference to Figs. 6 to 8. First, a comparative example for comparison with the communication station 10 according to the present embodiment will be described.

[0046] Fig. 6 is a diagram showing a comparative example for comparison with the operation of the communication station 10 according to the present embodiment. Note that, for simplification of description, communication delay is not considered here.

[0047] Reference time information distribution from <1> to <2> will be described below. Communication station 1 recognizes itself as the previous GM station, and transmits (3) reference time information 50 including "reference time: value of internal time counter (1:00)" and "clock ratio with GM station: 0".

[0048] Communication station 2 calculates the clock ratio with an adjacent station (-1 / 61) in advance based on the internal time interval at the transmission of communication station 1 (e.g., 1:00 = 2:00 - 1:00) measured by the (1) detection response signal and the internal time interval at the reception of communication station 2 (e.g., 1:01 = 2:02 - 1:01). Thereafter, when receiving the (3) reference time information, communication station 2 sets the reference time (1:00) to an estimated time counter. Further, communication station 2 calculates the clock ratio with the GM station (-1 / 61) using the clock ratio with the adjacent station (-1 / 61) and the received clock ratio with the GM station (0). Then, communication station 2 counts the estimated time counter using the calculated clock ratio with the GM station (-1 / 61). Thereby, the estimated time counter of communication station 2 is synchronized with the internal counter of the GM station. When communication station 2 receives the (3) reference time information in the reference time information distribution <2>, it transmits (3) reference time information including "reference time (1:00)" and "clock ratio with GM station (-1 / 61)".

[0049] Communication station 3 calculates the clock ratio with an adjacent station (+2 / 59) in advance based on the internal time interval at the transmission of communication station 2 (e.g., 1:01 = 2:02 - 1:01) measured by the (1) detection response signal and the internal time interval at the reception of communication station 3 (e.g., 0:59 = 1:57 - 0:58). Thereafter, when receiving the (3) reference time information, communication station 3 sets the reference time (1:00) to an estimated time counter. Further, communication station 3 calculates the clock ratio with the GM station (+1 / 59) using the clock ratio with the adjacent station (+2 / 59) and the received clock ratio with the GM station (-1 / 61). Then, communication station 3 counts the estimated time counter using the calculated clock ratio with the GM station (+1 / 59). Thereby, the estimated time counter of communication station 3 is synchronized with the internal counter of the GM station. Communication station 3 transmits (3) reference time information including "reference time (1:00)" and "clock ratio with GM station (+1 / 59)".

[0050] As described above, communication stations 2 and 3 of the TR station derive estimated times based on the reference time and clock ratio distributed from communication station 1 of the GM station.

[0051] The standard time information distribution <3> to <4> after the GM station switchover will be explained. Standard time information distribution <3> to <4> shows the case when communication station 1 disconnects from communication system 500 and communication station 2 becomes the GM station.

[0052] Communication station 2 recognizes itself as a GM station and transmits (3) reference time information, which includes "reference time: value of internal time counter (3:03)" and "clock ratio with GM station: 0". Thus, in this comparative example, communication station 2 does not inherit the reference time and clock ratio of the previous GM station, communication station 1. The clock ratio is overwritten with 0.

[0053] Communication station 3 sets the reference time (3:03) to the estimated time counter. Communication station 3 also calculates the clock ratio with the GM station (+2 / 59) using the clock ratio with the adjacent station (+2 / 59) and the clock ratio with the received GM station (0). Then, communication station 2 uses the calculated clock ratio with the GM station (+2 / 59) to count the estimated time counter. In this comparative example, communication station 2, which is the later GM station, distributes its own communication station's internal time and clock ratio. However, these are not continuous with the internal time and clock ratio of communication station 1, which was the earlier GM station. Therefore, a time difference occurs at communication station 3.

[0054] Figure 7 shows an example of the operation of the communication station 10 according to this embodiment. As with Figure 6, the explanation in Figure 7 will be simplified by not considering communication delays. The distribution of reference time information <1> to <2> is the same as in Figure 6. The time estimation unit 120 of the communication station 2 estimates the time from the reference time information, which includes the reference time received from the communication station 1, which is the source of the reference time.

[0055] The standard time information distribution <3> to <4> after the GM station switchover will be explained. Standard time information distribution <3> to <4> shows the case when communication station 1 disconnects from communication system 500 and communication station 2 becomes the GM station.

[0056] Communication station 2 recognizes itself as the next GM station. Communication station 2 transmits (3) reference time information, which includes "reference time: value of estimated time counter (3:00)" and "clock ratio with GM station: (-1 / 61)". At this time, communication station 2 distributes the value of the estimated time counter, which is an estimate of the internal time of the previous GM station, as "reference time 51", rather than the value of the internal time counter. In addition, communication station 2 distributes the clock ratio with the previous GM station (-1 / 61), rather than the clock ratio with the GM station (0), as "clock ratio with GM station". In this way, communication station 2, the next GM station, inherits the reference time and clock ratio based on the internal time of communication station 1, the previous GM station.

[0057] Communication station 3, which is a TR station, sets the reference time (3:00) included in the reference time information as the estimated time counter. Communication station 3 also calculates a new clock ratio with the GM station (+1 / 59) using the clock ratio with the adjacent station (+2 / 59) and the clock ratio with the received GM station (-1 / 61). Alternatively, it may use the previously calculated clock ratio with the GM station (+1 / 59) as is. Communication station 3 counts the estimated time counter using the clock ratio with the GM station (+1 / 59). In this embodiment, communication station 2, a later GM station, distributes the estimated time based on the internal time of communication station 1, a earlier GM station, and the clock ratio based on communication station 1, a earlier GM station. This prevents time drift at communication station 3.

[0058] When the reference time information received from the source, communication station 1, is interrupted, the communication unit 110 of communication station 2 becomes a new source of reference time and transmits reference time information that includes the time continuously estimated by the time estimation unit 120 as the reference time. In this way, communication station 2 continues to estimate the time even if it stops receiving reference time information from communication station 1. Then, communication station 2 transmits reference time information that includes the estimated time, which is the time that it has continuously estimated, as the reference time. As described above, communication station 1, which is the previous GM station, transmits reference time information using its internal time. On the other hand, communication station 2, which becomes the next GM station, does not use its internal time and transmits reference time information using its estimated time. If communication station 3 becomes the next GM station after communication station 2, communication station 3 will estimate the estimated time of communication station 2. Similar to communication station 2, communication station 3, which becomes the next GM station, does not use its internal time and transmits reference time information using its estimated time.

[0059] Figure 8 shows an example where the communication station 10 according to this embodiment does not inherit the clock ratio. Similar to Figures 6 and 7, the explanation in Figure 8 will also be simplified by not considering communication delay.

[0060] When multiple communication stations use high-performance clocks that do not cause clock drift between them, it is not necessary to inherit the clock ratio. However, if the clock ratio is not inherited when there is even a slight clock drift, a time difference will occur as shown below. The reference time information distribution from <1> to <2> is the same as in Figure 6.

[0061] The standard time information distribution <3> to <4> after the GM station switchover will be explained. Standard time information distribution <3> to <4> shows the case when communication station 1 disconnects from communication system 500 and communication station 2 becomes the GM station.

[0062] Communication station 2 recognizes itself as the next GM station. Here, communication station 2 inherits the reference time based on the internal time of the previous GM station, communication station 1, but does not inherit the clock ratio. Therefore, the value of the estimated time counter at communication station 2 becomes (3:01). Then, communication station 2 transmits (3) reference time information, which includes "reference time: value of estimated time counter (3:01)" and "clock ratio with GM station: 0". As a result, a time difference occurs at communication station 3, as shown in Figure 8.

[0063] Figure 9 shows an example of the operation of the communication station 10 according to this embodiment, taking into account communication delays. As shown in Figure 9, even if there is a propagation delay between communication stations, time discrepancies can be prevented. Figure 8 specifically shows the following cases with propagation delays: • Propagation delay between station 1 and station 2: 0:10:00 • Propagation delay between station 1 and station 3: 0:20:00 • Propagation delay between station 2 and station 3: 0:15:00

[0064] To rephrase the operation of the communication station 10 described above, it is as follows: The time estimation unit 120 estimates the estimated time from the reference time received from the grandmaster station, which is the source of the reference time. The communication station 10 receives the reference time either directly from the grandmaster station or via another communication station from the grandmaster station.

[0065] If the reference time received from the grandmaster station is interrupted, the communications unit 110 becomes a new grandmaster station and transmits the estimated time, which has been continuously estimated by the time estimation unit 120, as the reference time to other communications stations. The communications unit 110 determines whether or not it is the new grandmaster station, and if it determines that it is the new grandmaster station, it transmits the reference time to other communications stations.

[0066] Furthermore, the time estimation unit 120 calculates the clock ratio between the internal time of the grandmaster station and the local communication station, and transmits the clock ratio to other communication stations after the local communication station becomes the new grandmaster station.

[0067] ***Other Configurations*** <Modification> In this embodiment, the functions of the communication unit 110 and the time estimation unit 120 are implemented in software. As a modification, the functions of the communication unit 110 and the time estimation unit 120 may be implemented in hardware. Specifically, the communication station 10 includes a processing circuit 909 instead of a processor 910.

[0068] Figure 10 shows an example of the hardware configuration of a communication station 10 according to a modified example of this embodiment. The communication station 10 includes a processing circuit 909 instead of a processor 910, a processor 910 and memory 921, a processor 910 and auxiliary storage device 922, or a processor 910, memory 921 and auxiliary storage device 922. The processing circuit 909 is hardware that realizes at least a part of each component of the communication station 10. The processing circuit 909 may be dedicated hardware, or it may be a processor that executes a program stored in memory 921.

[0069] If the processing circuit 909 is dedicated hardware, specific examples of the processing circuit 909 include a single circuit, a composite circuit, a programmed processor, a parallel programmed processor, an ASIC (Application Specific Integrated Circuit), an FPGA (Field Programmable Gate Array), or a combination thereof. The communication station 10 may also have multiple processing circuits that substitute for the processing circuit 909. The multiple processing circuits share the role of the processing circuit 909.

[0070] In the communication station 10, some functions may be implemented by dedicated hardware, while the remaining functions may be implemented by software or firmware.

[0071] The processing circuit 909 can be implemented, in specific examples, by hardware, software, firmware, or a combination thereof. The processor 910, memory 921, auxiliary storage device 922, and processing circuit 909 are collectively referred to as the "processing circuitry." In other words, the functions of each functional component of the communication station 10 are implemented by the processing circuitry.

[0072] ***Explanation of the Effects of This Embodiment*** Normally, in a communication station, after a GM station switchover, the switched-out GM station distributes time information from the internal clock of the switched-out GM station. On the other hand, in this embodiment, after a GM station switchover, the switched-out GM station distributes time information estimated by inheriting the estimated time of the previous GM station, i.e., the GM station at the start of communication, and the clock ratio with the previous GM station. This allows the time information distributed by the previous GM station to be continued. As a result, with the communication station according to this embodiment, even if one communication station becomes unable to communicate, time synchronization can be continued throughout the entire network 400 while preventing time drift. In other words, the communication station according to this embodiment can provide a highly redundant and time-shift-free communication system.

[0073] In Embodiment 1 described above, each part of the communication station was described as an independent functional block. However, the configuration of the communication station does not have to be as described in the above embodiment. The functional blocks of the communication station can be configured in any way as long as they can realize the functions described in the above embodiment. Also, the communication station does not have to be a single device, but a system composed of multiple devices. Furthermore, multiple parts of Embodiment 1 may be combined and implemented. Alternatively, only one part of Embodiment 1 may be implemented. In addition, Embodiment 1 may be combined and implemented in any way, either as a whole or in part. That is to say, in Embodiment 1, it is possible to freely combine each embodiment, modify any component of each embodiment, or omit any component in each embodiment.

[0074] The embodiments described above are essentially preferred examples and are not intended to limit the scope of the Disclosure, the scope of the Applications of the Disclosure, or the scope of Uses of the Disclosure. The embodiments described above can be modified in various ways as needed. For example, the procedures described using flowcharts or sequence diagrams may be modified as appropriate.

[0075] The various aspects of this disclosure are summarized below as an appendix.

[0076] (Note 1) A communication station comprising: a time estimation unit that estimates an estimated time from the reference time received from a grandmaster station which is the source of the reference time; and a communication unit that, when the reference time received from the grandmaster station is interrupted, becomes a new grandmaster station and transmits the estimated time, which is continuously estimated by the time estimation unit, to other communication stations as the reference time. (Note 2) A communication station according to Note 1 that receives the reference time directly from the grandmaster station or receives it from the grandmaster station via another communication station. (Note 3) A communication station according to Note 1 or Note 2, wherein the communication unit determines whether the communication station is the new grandmaster station, and if it determines that the communication station is the new grandmaster station, transmits the reference time to other communication stations. (Note 4) A communication station according to any one of Notes 1 to 3, wherein the time estimation unit calculates the clock ratio of the internal time of the grandmaster station and the communication station itself, and after becoming a new grandmaster station, transmits the clock ratio to other communication stations. (Note 5) A time synchronization method comprising: a time estimation step of estimating an estimated time from a reference time received from a source of reference time; and a communication step of becoming a new source of reference time and transmitting the estimated time that has been continuously estimated in the time estimation step as the reference time when the reference time received from the source is interrupted. (Note 6) A time synchronization program that causes a computer to perform a time estimation process of estimating an estimated time from a reference time received from a source of reference time; and a communication process of becoming a new source of reference time and transmitting the estimated time that has been continuously estimated in the time estimation process as the reference time when the reference time received from the source is interrupted.(Note 7) A communication station included in a communication system comprising a plurality of communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a subsequent grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, the communication station comprising: a time estimation unit which estimates the time from reference time information including the reference time received from the source of the reference time; and a communication unit which, when the reference time information received from the source is interrupted, transmits to other communication stations reference time information including the estimated time which is the time that the time estimation unit has been continuously estimating as the reference time of the communication system, as the reference time of the communication system. (Note 8) The communication station according to Note 7, wherein the communication unit determines whether or not the communication station is the subsequent grandmaster station, and if it is determined that the communication station is the subsequent grandmaster station, transmits to other communication stations the reference time information including the estimated time as the reference time of the communication system. (Note 9) The communication unit, upon receiving the reference time information transmitted from the other communication station, sets the reference time included in the reference time information into an estimated time counter, and the time estimation unit counts the value of the estimated time counter as the estimated time, as described in Note 17 or Note 8. (Note 10) The communication unit, upon determining that its own communication station is the later grandmaster station, transmits the reference time information to the other communication station, including the estimated time which is the value of the estimated time counter and the later clock ratio which is the clock ratio between the previous grandmaster station and the communication station itself. (Note 11) The time estimation unit, upon receiving the reference time information, calculates the clock ratio between the previous grandmaster station and the communication station itself as the later clock ratio using the reference time included in the reference time information, the previous clock ratio which is the clock ratio included in the reference time information, and the internal time of the communication station itself, and counts the value of the estimated time counter as the estimated time based on the later clock ratio, as described in Note 10.(Note 12) The communication unit periodically transmits a grandmaster station selection signal for selecting the grandmaster station of the communication system, determines whether it is a grandmaster station and whether it has received selection information for a grandmaster station that has previously stored a higher priority than it, determines that it is the next grandmaster station if it has received selection information for a grandmaster station that has previously stored a higher priority than it, and determines that it is the previous grandmaster station if it has not received selection information for a grandmaster station that has previously stored a higher priority than it. (Note 13) The communication unit, when it determines that it is the previous grandmaster station, transmits the reference time information, which includes the internal time of the previous grandmaster station as the reference time, to the other communication station. (Note 14) A communication system comprising a plurality of communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a subsequent grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, wherein each of the plurality of communication stations comprises a time estimation unit which estimates the time from reference time information which includes the reference time received from the source of the reference time, and a communication unit which, when the reference time information that was being received from the source is interrupted, becomes a new source of reference time and transmits reference time information which includes the estimated time which is the time that the time estimation unit has been continuously estimating as the reference time of the communication system to other communication stations. (Note 15) A time synchronization method used for a communication station included in a communication system comprising multiple communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a subsequent grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, wherein a computer estimates the time from reference time information including the reference time received from the source of the reference time, and when the reference time information that was being received from the source is interrupted, transmits reference time information to other communication stations which includes the estimated time, which is the time that the computer has been continuously estimating as the reference time of the communication system, as the reference time of the communication system.(Note 16) A time synchronization program used in a communication station included in a communication system comprising multiple communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, the program causes the communication station, which is a computer, to perform a time estimation process which estimates the time from reference time information including the reference time received from the source of the reference time, and a communication process which, when the reference time information received from the source is interrupted, becomes a new source of reference time and transmits reference time information to other communication stations which includes the estimated time, which is the time that has been continuously estimated in the time estimation process, as the reference time of the communication system.

[0077] 10 Communication station, 31 Estimated time, 41 Internal time, 50 Reference time information, 51 Reference time, 80 Signal line, 90 Clock ratio, 91 Previous clock ratio, 92 Next clock ratio, 100 GM station, 101 Previous GM station, 102 Next GM station, 110 Communication unit, 120 Time estimation unit, 130 Estimated time counter, 140 Internal time counter, 400 Network, 500 Communication system, 909 Processing circuit, 910 Processor, 921 Memory, 922 Auxiliary storage device, 930 Input / output interface, 950 Communication interface.

Claims

1. A communication station comprising: a time estimation unit that estimates an estimated time from the reference time received from a grandmaster station which is the source of the reference time; and a communication unit that, when the reference time received from the grandmaster station is interrupted, becomes a new grandmaster station and transmits the estimated time, which is continuously estimated by the time estimation unit, to other communication stations as the reference time.

2. The communication station according to claim 1, which receives the reference time directly from the grandmaster station or receives it from the grandmaster station via another communication station.

3. The communication unit determines whether its own communication station is the new grandmaster station, and if it determines that its own communication station is the new grandmaster station, transmits the reference time to other communication stations, as described in claim 1 or 2.

4. The time estimation unit calculates the clock ratio of the internal time of the grandmaster station and the communication station itself, and after becoming a new grandmaster station, transmits the clock ratio to other communication stations, according to any one of claims 1 to 3.

5. A time synchronization method comprising: a time estimation step of estimating an estimated time from a reference time received from a source of reference time; and a communication step of becoming a new source of reference time when the reference time received from the source is interrupted, and transmitting the estimated time that has been continuously estimated in the time estimation step as the reference time.

6. A time synchronization program that causes a computer to perform a time estimation process that estimates an estimated time from a reference time received from a source of reference time, and a communication process that, when the reference time received from the source is interrupted, becomes a new source of reference time and transmits the estimated time that has been continuously estimated by the time estimation process as the reference time.

7. A communication station included in a communication system comprising a plurality of communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a subsequent grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, the communication station comprising: a time estimation unit which estimates the time from reference time information including the reference time received from the source of the reference time; and a communication unit which, when the reference time information received from the source is interrupted, becomes a new source of reference time and transmits reference time information to other communication stations which includes the estimated time, which is the time continuously estimated by the time estimation unit, as the reference time of the communication system.

8. The communication unit determines whether or not its own communication station is the later grandmaster station, and if it determines that its own communication station is the later grandmaster station, it transmits the reference time information, which includes the estimated time as the reference time of the communication system, to other communication stations, according to claim 7.

9. The communication station according to claim 7 or 8, wherein when the communication unit receives the reference time information transmitted from the other communication station, it sets the reference time included in the reference time information into an estimated time counter, and the time estimation unit counts the value of the estimated time counter as the estimated time.

10. The communication station according to claim 9, wherein when the communication unit determines that its own communication station is the later grandmaster station, it transmits the reference time information, which includes the estimated time being the value of the estimated time counter and the later clock ratio being the clock ratio between the earlier grandmaster station and its own communication station, to the other communication station.

11. The communication station according to claim 10, wherein when the time estimation unit receives the reference time information, it uses the reference time included in the reference time information, the previous clock ratio which is the clock ratio included in the reference time information, and the internal time of the communication station to calculate the clock ratio between the previous grandmaster station and the communication station as the next clock ratio, and counts the value of the estimated time counter as the estimated time based on the next clock ratio.

12. The communication unit periodically transmits a grandmaster station selection signal for selecting a grandmaster station of the communication system, determines whether it is a grandmaster station and whether it has received selection information for a grandmaster station that has previously stored a higher priority than it, determines that it is the next grandmaster station if it has received selection information for a grandmaster station that has previously stored a higher priority than it, and determines that it is the previous grandmaster station if it has not received selection information for a grandmaster station that has previously stored a higher priority than it.

13. The communication station according to any one of claims 7 to 12, wherein the communication unit determines that its own communication station is the former grandmaster station and transmits the reference time information, which includes the internal time of the former grandmaster station as the reference time, to the other communication station.

14. A communication system comprising a plurality of communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a subsequent grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, wherein each of the plurality of communication stations comprises: a time estimation unit which estimates the time from reference time information which includes the reference time received from the source of the reference time; and a communication unit which, when the reference time information received from the source is interrupted, becomes a new source of reference time and transmits reference time information which includes the estimated time which is the time continuously estimated by the time estimation unit as the reference time of the communication system to other communication stations.

15. A time synchronization method used for a communication station included in a communication system comprising multiple communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a subsequent grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, wherein a computer estimates the time from reference time information including the reference time received from the source of the reference time, and when the reference time information received from the source is interrupted, transmits reference time information to other communication stations which includes the estimated time, which is the time that the computer has been continuously estimating as the reference time of the communication system, as the reference time of the communication system.

16. A time synchronization program used in a communication station included in a communication system comprising multiple communication stations, including a former grandmaster station which is the source of the reference time at the start of communication and a grandmaster station which is selected as the grandmaster station after the former grandmaster station has left, the program causes the communication station, which is a computer, to perform a time estimation process which estimates the time from reference time information including the reference time received from the source of the reference time, and a communication process which, when the reference time information received from the source is interrupted, becomes a new source of reference time and transmits reference time information to other communication stations which includes the estimated time, which is the time continuously estimated by the time estimation process, as the reference time of the communication system.

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