JP2015188159A - Slave node, time synchronization method, and computer program - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a technique capable of preventing deterioration in accuracy in time synchronization at a slave node without correcting time with an offset value having a large error.SOLUTION: A slave node 20 comprises: a communication unit 201 that transmits and receives a control message used for time synchronization processing, i.e. processing to synchronize time at the slave node with time at a master node 10 to and from a plurality of master nodes; and a time correction unit 206 that corrects time at the slave node on the basis of time information obtained when the communication unit has transmitted or received the control message.

Description

  The present invention relates to a time synchronization technique.

  In recent years, highly accurate time synchronization has been demanded in order to perform coordinated operations between a plurality of base stations. Therefore, PTP (Precision Time Protocol) defined by IEEE 1588 is known as a technique for synchronizing the times of a plurality of devices connected to the network with an accuracy of microseconds or less (see, for example, Non-Patent Document 1). In PTP, messages including time information are periodically exchanged between a master node and a slave node. The slave node calculates a time lag (Offset) of the slave node with respect to the master node from the time information at which the messages at the master node and the slave node are transmitted and received. Then, the slave node corrects the time of the slave node based on the calculated offset, and synchronizes the time of the slave node with the time of the master node.

“IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems,” IEEE Standard 1588-2008.

  In the PTP described above, time synchronization is performed on the assumption that the delay time from the master node to the slave node is equal to the delay time from the slave node to the master node. However, in a general network, a master node and a slave node are often connected via a relay device such as a router. Therefore, the master node and the slave node are affected by the queuing delay in the relay device. The delay time will fluctuate. In such a case, the offset value obtained when correcting the time of the slave node includes an error. That is, when the influence of the queuing delay or the like in the relay apparatus is large, an error included in the obtained offset value also increases. Therefore, the slave node may correct the time of the slave node with an offset value having a large error. When such a problem occurs, the accuracy of time synchronization of the slave node deteriorates. Such a problem is not limited to PTP but is common to all communication protocols that perform time synchronization.

  In view of the above circumstances, an object of the present invention is to provide a technique capable of suppressing a decrease in accuracy of time synchronization of a slave node.

  One aspect of the present invention is a communication unit that transmits and receives a control message used for time synchronization processing, which is processing for synchronizing time in a slave node to time in a master node, with the plurality of master nodes; A time correction unit that corrects the time of its own device based on time information acquired when the unit transmits and receives the control message.

  One aspect of the present invention is the slave node described above, further including a calculation unit that calculates a statistical value of a time difference between the time of each master node and the time of the own device based on the acquired time information, The time correction unit corrects the time of the own device based on the calculated statistical value.

  One aspect of the present invention is the slave node described above, in which the calculation unit calculates the master node time and the own device time in the predetermined period based on the time information acquired during the predetermined period. A first statistical value that is a statistical value of a time difference with respect to each master node, and based on the calculated first statistical value for each master node, the time of each master node and the time of its own device, A second statistical value that is a statistical value of the time difference is calculated.

  One aspect of the present invention is the slave node described above, wherein the communication unit further receives the control message including a value indicating the quality of the time source of each master node during the time synchronization processing, and the calculation unit includes: The time difference between the time of the master node and the time of its own device is calculated for each master node based on the acquired time information, and the received control is obtained with respect to the calculated time difference for each master node. After weighting with a value representing the quality of the time source included in the message, the statistical value is calculated based on the weighted time difference for each master node.

  One aspect of the present invention is the slave node described above, wherein the communication unit further receives the control message including a value indicating the quality of the time source of each master node during the time synchronization processing, and the calculation unit includes: Based on the time information acquired during a predetermined period, a first statistical value that is a statistical value of a time difference between the time of the master node and the time of the own apparatus in the predetermined period is determined for each master node. The first statistical value for each master node calculated is weighted with a value representing the quality of the time source included in the received control message, and then the weighted first statistical value is calculated. Based on the above, a second statistical value that is a statistical value of a time difference between the time of each master node and the time of its own device is calculated.

  One aspect of the present invention is the slave node described above, in which the calculation unit calculates the master node time and the own device time in the predetermined period based on the time information acquired during the predetermined period. The first statistical value, which is a statistical value of the time difference with respect to the master node, is calculated for each master node, and the calculated first statistical value for each master node is the time difference for each master node in a predetermined period. After weighting with the variance value, a second statistical value that is a statistical value of a time difference between the time of each master node and the time of the own device is calculated based on the weighted first statistical value.

  One aspect of the present invention is a communication step of transmitting / receiving a control message used for time synchronization processing, which is processing for synchronizing time in a slave node to time in a master node, with a plurality of master nodes; And a time correction step of correcting the time of the slave node based on time information acquired when the control message is transmitted and received in steps.

  One aspect of the present invention is a communication step of transmitting / receiving a control message used for time synchronization processing, which is processing for synchronizing time in a slave node to time in a master node, with a plurality of master nodes; A computer program for causing a computer to execute a time correction step of correcting the time of the slave node based on time information acquired when the control message is transmitted and received in steps.

  According to the present invention, it is possible to suppress a decrease in time synchronization accuracy of the slave node.

It is a figure which shows the system configuration | structure of the time synchronization system 100 of this invention. 2 is a schematic block diagram of a master node 10 and a slave node 20. FIG. It is a sequence diagram showing the operation example of the communication sequence of the time synchronous process in the 1st operation example of this invention. It is a flowchart which shows the flow of a process of the slave node 20 in the 1st operation example of this invention. It is a sequence diagram showing the operation example of the communication sequence of the time synchronous process in the 2nd operation example of this invention. It is a flowchart which shows the flow of a process of the slave node 20 in the 2nd operation example of this invention. It is a sequence diagram showing the operation example of the communication sequence of the time synchronous process in the 3rd operation example of this invention. It is a flowchart which shows the flow of a process of the slave node 20 in the 3rd operation example of this invention. It is a sequence diagram showing the operation example of the communication sequence of the time synchronous process in the 4th operation example of this invention. It is a flowchart which shows the flow of a process of the slave node 20 in the 4th operation example of this invention. It is a sequence diagram showing the operation example of the communication sequence of the time synchronous process in the 5th operation example of this invention. It is a figure showing transition of the time difference between nodes for every master node 10 computed during predetermined period T0. It is a flowchart which shows the flow of a process of the slave node 20 in the 5th operation example of this invention.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.
FIG. 1 is a diagram showing a system configuration of a time synchronization system 100 of the present invention. The time synchronization system 100 of the present invention includes a master node 10 (10-1 and 10-2) and a slave node 20. The master node 10-1 and the slave node 20 are communicably connected to each other via the network 30-1. The master node 10-2 and the slave node 20 are communicably connected to each other via the network 30-2. Although FIG. 1 shows a configuration in which the time synchronization system 100 includes two master nodes 10, the time synchronization system 100 may be configured to include three or more master nodes 10. 1 shows a configuration in which the time synchronization system 100 includes one slave node 20, the time synchronization system 100 may be configured to include two or more slave nodes 20.

  The master node 10 periodically transmits and receives PTP messages (control messages) to and from the slave node 20. The PTP message is a control message (control packet) used for time synchronization processing, and is, for example, an Announce message, Sync message, Follow_up message, Delay_Request message, and Delay_Response message. The time synchronization process is a process for synchronizing the time at the slave node 20 with the time at the master node 10.

  The Announce message is a message for notifying other devices of the status information of the device itself. For example, the Announce message includes Clockclass information (hereinafter referred to as “quality information”) indicating the quality of the time source of the master node 10. Clockclass information is information indicating the quality of the time source of the master node 10 in 255 stages from 1 to 255, and the smaller the number, the better the quality of the time source. That is, when the clockclass information is “1”, it indicates that the quality of the time source of the master node 10 is the best, and when the clockclass information is “255”, the quality of the time source of the master node 10 is the worst. Represents that.

  The Sync message is a message transmitted to start the time synchronization operation. The Follow_up message is a message transmitted to notify the time information of the transmission time of the Sync message after the Sync message is transmitted. The Delay_Request message is a message that is transmitted in order to request the Delay_Response message from the master node 10 after the slave node 20 receives the Follow_up message transmitted from the master node 10. The Delay_Response message is a message transmitted as a response to the Delay_Request message.

The slave node 20 corrects the time (hereinafter referred to as “slave time”) of its own device (slave node 20) based on time information obtained when a PTP message is transmitted / received to / from each master node 10. .
The network 30-1 may be a network configured in any way. For example, the network 30-1 may be configured using a LAN (Local Area Network).
The network 30-2 may be a network configured in any way. For example, the network 30-2 may be configured using a LAN.

FIG. 2 is a schematic block diagram of the master node 10 and the slave node 20.
First, a specific functional configuration of the master node 10 will be described. The master node 10 includes a CPU (Central Processing Unit), a memory, an auxiliary storage device, and the like connected by a bus, and executes a time synchronization program. By executing the time synchronization program, the master node 10 functions as an apparatus including the master clock generation unit 101, the clock unit 102, the packet generation unit 103, and the communication unit 104. All or some of the functions of the master node 10 may be realized by using hardware such as an application specific integrated circuit (ASIC), a programmable logic device (PLD), or a field programmable gate array (FPGA). The time synchronization program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. The time synchronization program may be transmitted / received via a telecommunication line.

  The master clock generation unit 101 is configured by using a voltage variable crystal oscillator such as VCXO (Voltage controlled xtal oscillators), for example. The master clock generation unit 101 generates a master clock. Specifically, the master clock generation unit 101 determines a time width of 1 second in the master node 10. Note that the master clock generation unit 101 may exist outside the master node 10.

  The clock unit 102 determines the master time according to the master clock generated by the master clock generation unit 101. Specifically, the clock unit 102 determines what hour, minute, and second in the master node 10. The clock unit 102 outputs the time information of the master time to the packet generation unit 103.

  The packet generator 103 generates various packets. The packet generated by the packet generation unit 103 is, for example, an Announce message, Sync message, Follow_up message, Delay_Response message, or the like. The packet generation unit 103 adds the quality information of the time source of the master node 10 when generating the Announce message. The packet generation unit 103 periodically generates a Sync message. The packet generation unit 103 transmits a Sync message to the slave node 20 via the communication unit 104, and refers to the clock unit 102 at substantially the same time as the transmission time of the Sync message (hereinafter referred to as “Sync transmission time”) T1k (k Is an integer of 1 or more. Further, for example, the packet generation unit 103 generates a Follow_up message storing the Sync transmission time T1k after transmitting the Sync message. The packet generation unit 103 transmits a Follow_up message to the slave node 20 via the communication unit 104.

  Further, the packet generation unit 103 records the reception time (hereinafter referred to as “Delay reception time”) T4k of the Delay_Request message received by the communication unit 104 with reference to the clock unit 102. Thereafter, the packet generation unit 103 generates a Delay_Response message that stores the recorded Delay reception time T4k, and transmits the Delay_Response message to the slave node 20 via the communication unit 104.

  The communication unit 104 transmits and receives PTP messages to and from the slave node 20. For example, the communication unit 104 receives a Delay_Request message from the slave node 20 and transfers it to the packet generation unit 103. For example, the communication unit 104 transmits an Announce message, a Sync message, a Follow_up message, and a Delay_Response message to the slave node 20.

Next, the functional configuration of the slave node 20 will be described.
The slave node 20 includes a CPU, a memory, an auxiliary storage device, and the like connected by a bus, and executes a time synchronization program. By executing the time synchronization program, the slave node 20 functions as an apparatus including the communication unit 201, the control unit 202, the synchronization processing unit 203, the clock unit 204, the calculation unit 205, and the time correction unit 206. All or some of the functions of the slave node 20 may be realized using hardware such as an ASIC, PLD, or FPGA. The time synchronization program may be recorded on a computer-readable recording medium. The computer-readable recording medium is, for example, a portable medium such as a flexible disk, a magneto-optical disk, a ROM, a CD-ROM, or a storage device such as a hard disk built in the computer system. The time synchronization program may be transmitted / received via a telecommunication line.

  The communication unit 201 transmits / receives a PTP message to / from each master node 10. For example, the communication unit 201 receives an Announce message, a Sync message, a Follow_up message, and a Delay_Response message from each master node 10. For example, the communication unit 201 transmits a Delay_Request message to each master node 10.

  The control unit 202 controls each functional unit of the slave node 20. The control unit 202 extracts the quality information of the time source of the master node 10 stored in the Announce message. After receiving the Follow_up message, the control unit 202 generates a Delay_Request message. Thereafter, the control unit 202 causes the communication unit 201 to transmit the generated Delay_Request message, and records the transmission time of the Delay_Request message (hereinafter referred to as “Delay transmission time”) T3k almost simultaneously with reference to the clock unit 204. Further, the control unit 202 records the reception time of the Sync message (hereinafter referred to as “Sync reception time”) T2k when the Sync message is transferred from the communication unit 201. In addition, the control unit 202 extracts and records the Sync transmission time T1k stored in the Follow_up message. Further, the control unit 202 extracts and records the delay reception time T4k stored in the delay_response message.

The synchronization processing unit 203 determines a time width of 1 second in the slave node 20. Specifically, the synchronization processing unit 203 determines a time width of 1 second in the slave node 20 by generating a slave clock based on the Sync message received by the communication unit 201. The generated slave clock is synchronized with the master clock of the master node 10. The synchronization processing unit 203 calculates the difference between the time stamp generated from its own clock and the time stamp received from the master node 10, and any configuration can adjust its own clock based on the calculated difference. It may be a simple configuration.
The clock unit 204 determines the slave time according to the slave clock generated by the synchronization processing unit 203. Specifically, the clock unit 204 determines what hour, minute, and second in the slave node 20. The clock unit 204 outputs the time information of the slave time to the control unit 202.

The calculation unit 205 calculates a statistical value of the time difference between the master time and the slave time of each master node 10 based on the time information acquired when the communication unit 201 transmits / receives the PTP message. The statistical value is, for example, an average value, a maximum value, a minimum value, a mode value, or the like. In the following description, an average value will be described as an example of a statistical value. Hereinafter, the operation of the calculation unit 205 will be described. The slave node 20 calculates the time difference between the master time of the master node 10 and the slave time (hereinafter referred to as “inter-node time difference”) for each connected master node 10. Then, the slave node 20 calculates an average value of the inter-node time differences (hereinafter referred to as “time difference average value”) based on the calculated inter-node time difference for each master node 10.
This is the end of the description of the operation of the calculation unit 205.
The time correction unit 206 corrects the slave time based on the time difference average value calculated by the calculation unit 205.
Hereinafter, specific operation examples (first operation example to fifth operation example) of the time synchronization system 100 of the present invention will be described.

[First operation example]
FIG. 3 is a sequence diagram showing an operation example of a communication sequence of time synchronization processing in the first operation example of the present invention. In the description of FIG. 3, a case where the number of master nodes 10 is two (master node 10-1 and master node 10-2) and the number of slave nodes 20 is one will be described as an example.
The master node 10-1 periodically transmits a Sync message to the slave node 20 (step S101). The master node 10-1 records the Sync transmission time T11 (step S102). Next, the master node 10-1 transmits a Follow_up message to the slave node 20 (step S103). At this time, the master node 10-1 stores the Sync transmission time T11 in the Follow_up message.

  When receiving the Sync message transmitted from the master node 10-1, the slave node 20 records the Sync reception time T21 using this reception process as a trigger (Step S104). Next, the slave node 20 receives the Follow_up message transmitted from the master node 10-1, extracts the Sync transmission time T11 stored in the Follow_up message, and records it.

  The master node 10-2 periodically transmits a Sync message to the slave node 20 (step S105). The master node 10-1 records the Sync transmission time T12 (step S106). Next, the master node 10-2 transmits a Follow_up message to the slave node 20 (step S107). At this time, the master node 10-2 stores the Sync transmission time T12 in the Follow_up message.

  When receiving the Sync message transmitted from the master node 10-2, the slave node 20 records the Sync reception time T22 using this reception process as a trigger (Step S108). Next, the slave node 20 receives the Follow_up message transmitted from the master node 10-2, and extracts and records the Sync transmission time T12 stored in the Follow_up message.

  Next, the slave node 20 transmits a Delay_Request message to the master node 10-1 (step S109). Then, the slave node 20 records the delay transmission time T31 (step S110). When receiving the Delay_Request message, the master node 10-1 records the Delay reception time T41 using this reception process as a trigger (Step S111).

  In addition, the slave node 20 transmits a Delay_Request message to the master node 10-2 (Step S112). Then, the slave node 20 records the delay transmission time T32 (step S113). When receiving the Delay_Request message, the master node 10-2 records the Delay reception time T42 using this reception process as a trigger (Step S114).

  Next, the master node 10-1 transmits a Delay_Response message to the slave node 20 (step S115). At this time, the master node 10-1 stores the Delay reception time T41 in the Delay_Response message. When the slave node 20 receives the Delay_Response message transmitted from the master node 10-1, the slave node 20 extracts and records the Delay reception time T41 stored in the Delay_Response message.

  The master node 10-2 transmits a Delay_Response message to the slave node 20 (step S116). At this time, the master node 10-2 stores the Delay reception time T42 in the Delay_Response message. When the slave node 20 receives the Delay_Response message transmitted from the master node 10-2, the slave node 20 extracts and records the Delay reception time T42 stored in the Delay_Response message.

スレーブノード２０は、算出した時刻差平均値ａｖｅに基づいてスレーブ時刻を補正する（ステップＳ１１８）。 The slave node 20 performs time information (Sync transmission times T11 and T12, Sync reception times T21 and T22, Delay transmission times T31 and T32, Delay reception time) with the master nodes 10-1 and 10-2 by the above-described processing. T41 and T42) are acquired. The slave node 20 calculates the time difference average value ave based on the acquired time information (step S117). The time difference average value ave is calculated based on the following formula 1, for example.

The slave node 20 corrects the slave time based on the calculated time difference average value ave (step S118).

  The time of the slave node 20 is corrected by the process described above. In the time synchronization process, as described above, a series of exchanges related to time synchronization is performed between the slave node 20 and the master node 10. A series of exchanges related to time synchronization indicates that a Sync message, a Follow_up message, a Delay_Request message, and a Delay_Response message are transmitted and received between the slave node 20 and the master node 10.

FIG. 4 is a flowchart showing a processing flow of the slave node 20 in the first operation example of the present invention.
The communication unit 201 of the slave node 20 receives the Sync message transmitted from the master node 10 (Step S201). When receiving the Sync message from the master node 10, the communication unit 201 transfers the received Sync message to the control unit 202. When the Sync message is transferred, the control unit 202 refers to the clock unit 204 and records the Sync reception time T2k.

  Next, the communication unit 201 receives a Follow_up message transmitted from the master node 10 (step S202). When receiving the Follow_up message from the master node 10, the communication unit 201 transfers the received Follow_up message to the control unit 202. The control unit 202 extracts and records the Sync transmission time T1k stored in the Follow_up message.

  Thereafter, the control unit 202 generates a Delay_Request message and transmits the Delay_Request message to the master node 10 via the communication unit 201 (step S203). At this time, the control unit 202 refers to the clock unit 204 and records the delay transmission time T3k (step S204). Thereafter, the communication unit 201 receives a Delay_Response message transmitted from the master node 10 (step S205). When receiving the Delay_Response message from the master node 10, the communication unit 201 transfers the received Delay_Response message to the control unit 202. The control unit 202 extracts and records the Delay reception time T4k stored in the Delay_Response message.

The control unit 202 determines whether time information has been acquired with all the connected master nodes 10 (step S206). When the time information is not acquired with all the connected master nodes 10 (step S206—NO), the slave node 20 repeatedly executes the processes after step S201.
On the other hand, when time information is acquired with all the connected master nodes 10 (step S206-YES), each time information acquired with each master node 10 which the control part 202 has recorded. (Sync transmission time T1k, Sync reception time T2k, Delay transmission time T3k, Delay reception time T4k) are output to calculation section 205.

  The calculating unit 205 calculates a time difference average value ave based on each time information output from the control unit 202 (step S207). The time correction unit 206 corrects the slave time based on the calculated time difference average value ave (step S208).

  According to the slave node 20 configured as described above, even if fluctuation occurs in the delay time between the master node 10 and the slave node 20 due to the influence of queuing delay or the like in the relay device, it is correct. The possibility that the time of the slave node 20 is corrected at a time greatly deviated from the time is reduced. Specifically, the slave time is corrected by the average value of the inter-node time differences calculated based on the time information acquired with each of the plurality of master nodes 10. As described above, the slave time is corrected with the average value including the time difference between the slave time and the master time of the other master node 10, so that the slave time is corrected with a value greatly deviating from the correct time. The fear can be reduced. Therefore, it is possible to suppress a decrease in accuracy of time synchronization of the slave node 20.

式２のｎは、スレーブノード２０が接続しているマスターノード１０の台数を表す。 <Modification>
In this operation example, the formula (formula 1) for calculating the time difference average value ave when the number of master nodes 10 is two is shown, but when the number of master nodes 10 is three or more, The calculation unit 205 calculates the time difference average value ave based on the following Equation 2.

N in Equation 2 represents the number of master nodes 10 to which the slave node 20 is connected.

  In this operation example, after the slave node 20 acquires each time information with all the connected master nodes 10, that is, with a series of time synchronizations with all the master nodes 10. Although the configuration is shown in which the time difference average value ave is calculated after one exchange, the present invention is not limited to this. For example, the following processing may be performed. The slave node 20 is a node between the slave node 20 and the master node 10 in which a series of exchanges related to time synchronization are performed after a series of exchanges related to time synchronization is performed for each connected master node 10. The time difference is calculated. The slave node 20 repeatedly executes this process, calculates the inter-node time difference for each connected master node 10, and then calculates the time difference average value ave based on the calculated inter-node time difference. Hereinafter, a specific example will be described.

When the slave node 20 is connected to a plurality of (for example, two) master nodes 10, the slave node 20 transmits and receives PTP messages to and from each of the plurality of master nodes 10. When the slave node 20 acquires all the time information (Sync transmission time T11, Sync reception time T21, Delay transmission time T31, Delay reception time T41) with the master node 10-1, the slave node 20 obtains the following formula: 3, the inter-node time difference m1 between the master node 10-1 and the slave node 20 is calculated.

Similarly, when the slave node 20 acquires all the time information (Sync transmission time T12, Sync reception time T22, Delay transmission time T32, Delay reception time T42) with the master node 10-2, the slave node 20 The inter-node time difference m2 between the master node 10-2 and the slave node 20 is calculated based on the following Equation 4.

Through the processing described above, the slave node 20 calculates the inter-node time difference with all the connected master nodes 10. When the slave node 20 calculates inter-node time differences with all the master nodes 10, the slave node 20 calculates a time difference average value ave based on all the calculated inter-node time differences. The slave node 20 calculates the time difference average value ave based on the following formula 5, for example.

[Second operation example]
FIG. 5 is a sequence diagram showing an operation example of a communication sequence of time synchronization processing in the second operation example of the present invention. In the description of FIG. 5, a case where the number of master nodes 10 is two (master node 10-1 and master node 10-2) and the number of slave nodes 20 is one will be described as an example. Further, the processing similar to that in FIG. 3 is denoted by the same reference numerals as those in FIG. 3 in FIG.

As shown in FIG. 5, in the communication sequence of the time synchronization process in the second operation example, the processes from step S101 to step S116 are repeatedly executed during a predetermined period T0. That is, a series of exchanges related to time synchronization is performed between the master node 10-1 and the slave node 20 and between the master node 10-2 and the slave node 20 for a predetermined period T0. The number of times the slave node 20 performs a series of exchanges related to time synchronization with the master nodes 10-1 and 10-2 is calculated based on, for example, the following formulas 6 and 7.

  In Expression 6, x represents the number of times that the slave node 20 performs a series of exchanges related to time synchronization with the master node 10-1 during a predetermined period T0, and X represents the slave node 20 and the master node 10-1. Represents a cycle in which a series of exchanges related to time synchronization are performed. Y in Expression 7 represents the number of times the slave node 20 performs a series of exchanges related to time synchronization with the master node 10-2 during a predetermined period T0, and Y represents the slave node 20 and the master node 10-2. Represents a cycle in which a series of exchanges related to time synchronization are performed. Note that the number of times that the slave node 20 performs a series of exchanges related to time synchronization with each master node 10 during the predetermined period T0 may be the same for all the master nodes 10 or the master node. It may be determined in advance every ten.

The slave node 20 performs a series of exchanges related to time synchronization with each master node 10 by the number of times corresponding to the number of times calculated for each master node 10. Thereby, the slave node 20 acquires the time information in the predetermined period T0 for each master node 10. When the predetermined period T0 elapses, the slave node 20 determines, based on the time information for each master node 10 acquired during the predetermined period T0, an average value of inter-node time differences in the predetermined period T0 (hereinafter, “period average”). (Referred to as “value”) (first statistical value) is calculated for each master node 10 (step S301). For example, the period average value M1 between the master node 10-1 and the slave node 20 is calculated based on the following Expression 8. Further, for example, the period average value M2 between the master node 10-2 and the slave node 20 is calculated based on the following Expression 9.

スレーブノード２０は、算出した時刻差平均値ａｖｅ１に基づいてスレーブ時刻を補正する（ステップＳ３０３）。
上述した処理によってスレーブノード２０の時刻が補正される。 (1) in Equation 8 and Equation 9 represents the number of series of exchanges related to time synchronization at the time when each time information is acquired during the predetermined period T0. That is, the value of (l) is (1) in the time information acquired in the series of exchanges related to the first time synchronization. Thereafter, the slave node 20 calculates a time difference average value ave1 (second statistical value) based on the period average values M1 and M2 calculated for each master node 10 (step S302). The time difference average value ave1 is calculated based on the following Expression 10, for example.

The slave node 20 corrects the slave time based on the calculated time difference average value ave1 (step S303).
The time of the slave node 20 is corrected by the process described above.

FIG. 6 is a flowchart showing a process flow of the slave node 20 in the second operation example of the present invention. Also, processing similar to that in FIG. 4 is denoted by the same reference numerals as in FIG. 4 in FIG.
When the processing up to step S206 is completed and time information is acquired with all the master nodes 10 in step S206 (step S206—YES), the control unit 202 determines whether or not a predetermined period T0 has elapsed. Determination is made (step S401). When the predetermined period T0 has not elapsed (step S401—NO), the slave node 20 repeatedly executes the processes after step S201.

  On the other hand, when the predetermined period T0 has elapsed (step S401—YES), the calculation unit 205 calculates the average period value for each master node 10 based on the time information acquired during the predetermined period T0 (step S402). ). Thereafter, the calculation unit 205 calculates a time difference average value ave1 based on the calculated period average value for each master node 10 (step S403). The time correction unit 206 corrects the slave time based on the calculated time difference average value ave1 (step S404).

  According to the slave node 20 configured as described above, even if fluctuation occurs in the delay time between the master node 10 and the slave node 20 due to the influence of queuing delay or the like in the relay device, it is correct. The possibility that the time of the slave node 20 is corrected at a time greatly deviated from the time is reduced. Specifically, the slave time is an average value of the period average values for each master node 10 calculated based on a plurality of time information respectively acquired with the plurality of master nodes 10 during a predetermined period T0. It is corrected. Therefore, the slave time is corrected by the average value of the time difference between the slave time and the master time of each master node, which is calculated from the time information acquired when a series of exchanges related to time synchronization is performed once. It is possible to correct the time closer to the correct time. Therefore, it is possible to suppress a decrease in accuracy of time synchronization of the slave node 20.

式１１のｎは、スレーブノード２０が接続しているマスターノード１０の台数を表す。 <Modification>
In this operation example, the equation (Equation 10) for calculating the time difference average value ave1 when the number of master nodes 10 is two is shown, but when the number of master nodes 10 is three or more, The calculation unit 205 calculates the time difference average value ave1 based on the following Expression 11.

N in Expression 11 represents the number of master nodes 10 to which the slave node 20 is connected.

  Further, in this operation example, a configuration is shown in which the slave node 20 stores all time information acquired during the predetermined period T0 and calculates the period average value and the time difference average value ave1 after the predetermined period T0 has elapsed. However, it need not be limited to this. For example, the following processing may be performed. The slave node 20 is a node between the slave node 20 and the master node 10 in which a series of exchanges related to time synchronization are performed after a series of exchanges related to time synchronization is performed for each connected master node 10. The time difference is calculated. The slave node 20 repeatedly executes this process for a predetermined period T0, and calculates the inter-node time difference in the predetermined period T0 for each master node 10. After the predetermined period T0 has elapsed, the slave node 20 calculates a period average value for each master node 10 based on the inter-node time difference for each master node 10 calculated during the predetermined period T0. Then, the slave node 20 calculates the time difference average value ave1 based on the calculated period average value for each master node 10. Hereinafter, a specific example will be described.

When the slave node 20 is connected to a plurality of (for example, two) master nodes 10, the slave node 20 transmits and receives PTP messages to and from each of the plurality of master nodes 10. When the slave node 20 acquires all the time information with the master node 10-1, the slave node 20 determines the inter-node time difference m1 between the master node 10-1 and the slave node 20 based on the following Expression 12. l) is calculated.

Similarly, when the slave node 20 acquires all the time information with the master node 10-2, the slave node 20 determines the time difference m2 between the master node 10-2 and the slave node 20 based on the following Expression 13. (L) is calculated.

その後、算出部２０５は、算出した期間平均値Ｍ１及びＭ２に基づいて時刻差平均値ａｖｅ１を上記式１０に基づいて算出する。 Through the processing described above, the slave node 20 calculates the inter-node time difference mk (l) with all the connected master nodes 10 during the predetermined period T0. After a predetermined period T0 has elapsed, the slave node 20 calculates a period average value Mk for each master node 10 based on the inter-node time difference mk (l) calculated during the predetermined period T0. For example, the slave node 20 calculates a period average value M1 of the inter-node time difference m1 (l) between the master node 10-1 and the slave node 20 during a predetermined period T0 based on the following Expression 14. For example, the slave node 20 calculates a period average value M2 of the inter-node time difference m2 (l) between the master node 10-2 and the slave node 20 during a predetermined period T0 based on the following Expression 15. .

After that, the calculation unit 205 calculates the time difference average value ave1 based on the above formula 10 based on the calculated period average values M1 and M2.

[Third operation example]
FIG. 7 is a sequence diagram showing an operation example of a communication sequence of time synchronization processing in the third operation example of the present invention. In the description of FIG. 7, a case where the number of master nodes 10 is two (master node 10-1 and master node 10-2) and the number of slave nodes 20 is one will be described as an example. Further, the processing similar to that in FIG. 3 is denoted by the same reference numerals as those in FIG. 3 in FIG.

  The master node 10-1 periodically transmits an Announce message to the slave node 20 (step S501). At this time, the master node 10-1 stores the quality information of the time source of the master node 10-1 in the Announce message. The slave node 20 receives the Announce message transmitted from the master node 10-1, and extracts and holds quality information stored in the Announce message.

  In addition, the master node 10-2 periodically transmits an Announce message to the slave node 20 (step S502). At this time, the master node 10-2 stores the quality information of the time source of the master node 10-2 in the Announce message. The slave node 20 receives the Announce message transmitted from the master node 10-2, extracts the quality information stored in the Announce message, and holds it. Thereafter, the processing from step S101 to step S116 is executed.

The slave node 20 in the third operation example performs quality information and time information (Sync transmission times T11 and T12, Sync messages) with the master nodes 10-1 and 10-2 by the above-described processing (processing from Step S501 to Step S116). Sync reception times T21 and T22, Delay transmission times T31 and T32, and Delay reception times T41 and T42) are acquired. The slave node 20 calculates the time difference average value ave2 based on the quality information and each time information (step S503). The time difference average value ave2 is calculated based on the following Expression 16, for example.

In Expression 16, a represents the quality of the time source of the master node 10-1, and b represents the quality of the time source of the master node 10-2. The slave node 20 corrects the slave time based on the calculated time difference average value ave2 (step S504).
The time of the slave node 20 is corrected by the process described above.

FIG. 8 is a flowchart showing a process flow of the slave node 20 in the third operation example of the present invention. Also, the processing similar to that in FIG. 4 is denoted by the same reference numerals as those in FIG. 4 in FIG.
The communication unit 201 of the slave node 20 receives the Announce message transmitted from the master node 10 (step S601). Upon receiving the Announce message from the master node 10, the communication unit 201 transfers the received Announce message to the control unit 202. The control unit 202 extracts and holds the quality information stored in the Announce message.

  Thereafter, when the processing from step S201 to step S205 is executed, the control unit 202 determines whether or not the quality information and time information have been acquired with all the connected master nodes 10 (step S602). . When quality information and time information have not been acquired with all the master nodes 10 (step S602-NO), the slave node 20 repeatedly executes the processing after step S601.

On the other hand, when quality information and time information are acquired with all the master nodes 10 (step S602-YES), the control unit 202 records the quality information acquired with each master node 10 and each The time information (Sync transmission time T1k, Sync reception time T2k, Delay transmission time T3k, Delay reception time T4k) is output to the calculation unit 205.
The calculation unit 205 calculates the time difference average value ave2 based on the quality information and each time information output from the control unit 202 (step S603). The time correction unit 206 corrects the slave time based on the calculated time difference average value ave2 (step S604).

  According to the slave node 20 configured as described above, even if fluctuation occurs in the delay time between the master node 10 and the slave node 20 due to the influence of queuing delay or the like in the relay device, it is correct. The possibility that the time of the slave node 20 is corrected at a time greatly deviated from the time is reduced. Specifically, the average value of the time difference between the slave time and the master time of each master node 10 calculated based on the time information acquired with each of the plurality of master nodes 10 is obtained for each master node 10. The slave time is corrected by an average value of values weighted by the quality of the time source. Therefore, it is possible to improve the possibility of realizing more accurate synchronization. For example, since the quality of the time source of the master node 10 may be deteriorated, synchronization with higher accuracy is realized by incorporating a high-quality one into the calculation of the time difference average value. Therefore, it is possible to suppress a decrease in accuracy of time synchronization of the slave node 20.

式１７のαｋは、マスターノード１０の時刻源の品質を表し、ここではマスターノード１０の時刻源の品質が高い場合、αｋの値は小さくなると定義している。算出部２０５は、ノード間時刻差の値が小さい順に、マスターノード１０の時刻源の品質が高い値を順番に重みづけの値として割り当ててもよいし、その他の順番でマスターノード１０の時刻源の品質を重みづけの値として割り当ててもよい。 <Modification>
In this operation example, the equation (Equation 16) for calculating the time difference average value ave2 when the number of master nodes 10 is two is shown, but the number of master nodes 10 is three or more (for example, n). In this case, the calculation unit 205 calculates the time difference average value ave2 based on the following Expression 17.

Αk in Expression 17 represents the quality of the time source of the master node 10, and here, when the quality of the time source of the master node 10 is high, the value of αk is defined to be small. The calculation unit 205 may assign values having higher quality of the time source of the master node 10 as weighting values in order from the smallest value of the time difference between nodes, or the time sources of the master node 10 in other orders. May be assigned as a weighting value.

In this operation example, the case where the quality of the time source of the master node 10 is a fixed value has been described as an example, but the quality of the time source of the master node 10 may change according to time.
In this operation example, after the slave node 20 acquires the quality information and each time information with all the connected master nodes 10, that is, with the quality information with all the master nodes 10. Although a configuration has been shown in which the time difference average value ave2 is calculated after a series of exchanges related to time synchronization that have been acquired and performed once, the present invention is not limited to this. For example, the following processing may be performed. The slave node 20 receives the Announce message for each connected master node 10, and acquires the time source quality information for each master node 10 from the received Announce message. In addition, the slave node 20 is connected between the master node 10 and the slave node that have performed a series of exchanges related to time synchronization after a series of exchanges related to time synchronization is performed for each connected master node 10. Calculate the time difference between nodes. The slave node 20 repeatedly executes this process, calculates the inter-node time difference for each connected master node 10, and then calculates the time difference average based on the calculated inter-node time difference and the acquired quality information. The value ave2 is calculated. Hereinafter, a specific example will be described.

When the slave node 20 is connected to a plurality of (for example, two) master nodes 10, the slave node 20 transmits and receives PTP messages to and from each of the plurality of master nodes 10. When the slave node 20 acquires all of the time source quality information (for example, a and b) and each time information with the master node 10-1, the slave node 20 determines that the master node 10-1 And the node time difference m1 between the slave node 20 and the slave node 20 is calculated.
Similarly, when the slave node 20 acquires all the quality information and each time information of the time source with the master node 10-2, the slave node 20 determines that the master node 10-2 and the slave node 20 are based on the above equation 4. The time difference m2 between the nodes is calculated.

Through the processing described above, the slave node 20 calculates the inter-node time difference with all the connected master nodes 10. When the slave node 20 calculates the inter-node time difference with all the master nodes 10, the slave node 20 calculates the inter-node time difference and the quality information (for example, a and b) of each master node 10. Based on this, the time difference average value ave2 is calculated. The slave node 20 calculates the time difference average value ave2 based on the following equation 18, for example.

[Fourth operation example]
FIG. 9 is a sequence diagram showing an operation example of a communication sequence of time synchronization processing in the fourth operation example of the present invention. In the description of FIG. 9, a case where the number of master nodes 10 is two (master node 10-1 and master node 10-2) and the number of slave nodes 20 is one will be described as an example. Further, processing similar to that in FIG. 7 is denoted by the same reference numerals as those in FIG.

  As shown in FIG. 9, in the communication sequence of the time synchronization process in the fourth operation example, after the slave node 20 receives the Announce message from the master nodes 10-1 and 10-2, for a predetermined period T0, The processing from step S101 to step S116 is repeatedly executed. That is, a series of exchanges related to time synchronization is performed between the master node 10-1 and the slave node 20 and between the master node 10-2 and the slave node 20 for a predetermined period T0. The number of times that the slave node 20 performs a series of exchanges related to time synchronization with the master nodes 10-1 and 10-2 is calculated based on, for example, the above formulas 6 and 7. Note that the number of times that the slave node 20 performs a series of exchanges related to time synchronization with each master node 10 during the predetermined period T0 may be the same for all the master nodes 10 or the master node. It may be determined in advance every ten.

  The slave node 20 performs a series of exchanges related to time synchronization with each master node 10 by the number of times corresponding to the number of times calculated for each master node 10. Thereby, the slave node 20 acquires the time information in the predetermined period T0 for each master node 10. When the predetermined period T0 elapses, the slave node 20 calculates the average period value for the predetermined period T0 for each master node 10 based on the time information for each master node 10 acquired during the predetermined period T0 (step S0). S701). For example, the average period value M1 between the master node 10-1 and the slave node 20 is calculated based on Equation 8 above. Further, for example, the average period value M2 between the master node 10-2 and the slave node 20 is calculated based on Equation 9 above.

スレーブノード２０は、算出した時刻差平均値ａｖｅ３に基づいてスレーブ時刻を補正する（ステップＳ７０３）。
上述した処理によってスレーブノード２０の時刻が補正される。 Thereafter, the slave node 20 calculates the time difference average value ave3 based on the average values M1 and M2 calculated for each master node 10 and the quality information of each master node 10 acquired from the master nodes 10-1 and 10-2. Is calculated (step S702). The time difference average value ave3 is calculated based on the following Expression 19, for example.

The slave node 20 corrects the slave time based on the calculated time difference average value ave3 (step S703).
The time of the slave node 20 is corrected by the process described above.

FIG. 10 is a flowchart showing a processing flow of the slave node 20 in the fourth operation example of the present invention. Further, the processing similar to that in FIG. 8 is denoted by the same reference numerals as those in FIG. 8 in FIG.
When the processing up to step S602 is completed and quality information and time information have been acquired with all the master nodes 10 in step S602 (step S602—YES), the control unit 202 has passed a predetermined period T0. Whether or not (step S801). When the predetermined period T0 has not elapsed (step S801—NO), the slave node 20 repeatedly executes the processes after step S201.

  On the other hand, when the predetermined period T0 has elapsed (step S801—YES), the calculation unit 205 calculates a period average value for each master node 10 based on the time information acquired during the predetermined period T0 (step S802). ). Thereafter, the calculation unit 205 calculates the time difference average value ave3 based on the calculated average period value for each master node 10 and the quality information of each master node 10 (step S803). The time correction unit 206 corrects the slave time based on the calculated time difference average value ave3 (step S804).

  According to the slave node 20 configured as described above, even if fluctuation occurs in the delay time between the master node 10 and the slave node 20 due to the influence of queuing delay or the like in the relay device, it is correct. The possibility that the time of the slave node 20 is corrected at a time greatly deviated from the time is reduced. Specifically, the average value of the period average values for each master node 10 calculated based on the plurality of time information respectively acquired with the plurality of master nodes 10 during the predetermined period T0 is set for each master node. The slave time is corrected by an average value of values weighted by the quality of the ten time sources. Therefore, it is possible to improve the possibility of realizing more accurate synchronization. For example, since the quality of the time source of the master node 10 may be deteriorated, synchronization with higher accuracy is realized by incorporating a high-quality one into the calculation of the time difference average value. Therefore, it is possible to suppress a decrease in accuracy of time synchronization of the slave node 20.

<Modification>
In this operation example, the equation (Equation 19) for calculating the time difference average value ave3 when the number of master nodes 10 is two is shown, but when the number of master nodes 10 is three or more, The calculation unit 205 calculates the time difference average value ave3 based on the expression represented by the average in the time interval T0 of Expression 17 above.

  Further, in this operation example, the configuration is shown in which the slave node 20 stores all the time information acquired during the predetermined period T0 and calculates the period average value and the time difference average value ave3 after the predetermined period T0 has elapsed. However, it need not be limited to this. For example, the following processing may be performed. The slave node 20 is a node between the slave node 20 and the master node 10 in which a series of exchanges related to time synchronization are performed after a series of exchanges related to time synchronization is performed for each connected master node 10. The time difference is calculated. The slave node 20 repeatedly executes this process for a predetermined period T0, and calculates the inter-node time difference in the predetermined period T0 for each master node 10. After the predetermined period T0 has elapsed, the slave node 20 calculates a period average value for each master node 10 based on the inter-node time difference for each master node 10 calculated during the predetermined period T0. Then, the slave node 20 calculates the time difference average value ave3 based on the calculated period average value for each master node 10 and the quality information of the time source of each master node 10. Hereinafter, a specific example will be described.

When the slave node 20 is connected to a plurality of (for example, two) master nodes 10, the slave node 20 transmits and receives PTP messages to and from each of the plurality of master nodes 10. Thereby, the slave node 20 acquires the quality information (for example, a and b) and time information of each master node 10. When the slave node 20 acquires all the time information with the master node 10-1, the slave node 20 determines the inter-node time difference m1 (l between the master node 10-1 and the slave node 20 based on the above equation 12. ) Is calculated.
Similarly, when the slave node 20 acquires all the time information with the master node 10-2, the slave node 20 determines the inter-node time difference between the master node 10-2 and the slave node 20 based on the above equation 13. m2 (l) is calculated.

Through the processing described above, the slave node 20 calculates the inter-node time difference mk (l) with all the connected master nodes 10 during the predetermined period T0. After a predetermined period T0 has elapsed, the slave node 20 calculates a period average value Mk for each master node 10 based on the inter-node time difference calculated during the predetermined period T0. For example, the slave node 20 calculates the period average value M1 of the inter-node time difference m1 (l) between the master node 10-1 and the slave node 20 during the predetermined period T0 based on the above equation 14. The slave node 20 calculates the period average value M2 of the inter-node time difference m2 (l) between the master node 10-2 and the slave node 20 during the predetermined period T0 based on the above equation 15.
After that, the calculation unit 205 calculates the time difference average value ave3 based on the equation 19 based on the calculated period average values M1 and M2 and quality information (for example, a and b).

[Fifth operation example]
FIG. 11 is a sequence diagram showing an operation example of a communication sequence of time synchronization processing in the fifth operation example of the present invention. In the description of FIG. 11, a case where the number of master nodes 10 is two (master node 10-1 and master node 10-2) and the number of slave nodes 20 is one will be described as an example. Further, processing similar to that in FIG. 5 is denoted by the same reference numerals as those in FIG. 5 in FIG.

  As shown in FIG. 11, in the communication sequence of the time synchronization process in the fifth operation example, the processes from step S101 to step S116 are repeatedly executed during a predetermined period T0. That is, a series of exchanges related to time synchronization is performed between the master node 10-1 and the slave node 20 and between the master node 10-2 and the slave node 20 for a predetermined period T0. The number of times that the slave node 20 performs a series of exchanges related to time synchronization with the master nodes 10-1 and 10-2 is calculated based on, for example, the above formulas 6 and 7. Note that the number of times that the slave node 20 performs a series of exchanges related to time synchronization with each master node 10 during the predetermined period T0 may be the same for all the master nodes 10 or the master node. It may be determined in advance every ten.

  The slave node 20 performs a series of exchanges related to time synchronization with each master node 10 by the number of times corresponding to the number of times calculated for each master node 10. Thereby, the slave node 20 acquires the time information in the predetermined period T0 for each master node 10. When the predetermined period T0 elapses, the slave node 20 calculates an average value for each master node 10 in the predetermined period T0 based on the time information for each master node 10 acquired during the predetermined period T0 (step S0). S901). For example, the average period value M1 between the master node 10-1 and the slave node 20 is calculated based on Equation 8 above. Further, for example, the average period value M2 between the master node 10-2 and the slave node 20 is calculated based on Equation 9 above.

Thereafter, the slave node 20 compares the period average value Mk (M1 and M2) calculated for each master node 10 and the inter-node time difference mk () for each series of exchanges related to time synchronization performed during the predetermined period T0. 1), a variance value Vk of the inter-node time difference mk (l) in a predetermined period T0 is calculated for each master node 10 (step S902). For example, the variance value V1 of the inter-node time difference m1 (l) in the predetermined period T0 between the master node 10-1 and the slave node 20 is calculated based on the following Expression 20. Further, for example, the variance value V2 of the inter-node time difference m2 (l) between the master node 10-2 and the slave node 20 during a predetermined period T0 is calculated based on the following Expression 21.

  X in Expression 20 represents the number of times that the slave node 20 performs a series of exchanges related to time synchronization with the master node 10-1 during the predetermined period T0. Y in Expression 21 represents the number of times that the slave node 20 performs a series of exchanges related to time synchronization with the master node 10-2 during the predetermined period T0. (L) in Expression 20 and Expression 21 represents the number of series of exchanges related to time synchronization at the time when each time information is acquired during the predetermined period T0.

スレーブノード２０は、算出した時刻差平均値ａｖｅ４に基づいてスレーブ時刻を補正する（ステップＳ９０４）。
上述した処理によってスレーブノード２０の時刻が補正される。 Thereafter, the slave node 20 calculates the time difference average value ave4 based on the variance value Vk (V1 and V2) calculated for each master node 10 and the period average value Mk (M1 and M2) (step S903). The time difference average value ave4 is calculated based on the following Expression 22, for example.

The slave node 20 corrects the slave time based on the calculated time difference average value ave4 (step S904).
The time of the slave node 20 is corrected by the process described above.

FIG. 12 is a diagram illustrating the transition of the inter-node time difference for each master node 10 calculated during the predetermined period T0.
In FIG. 12, the vertical axis represents the inter-node time difference mk, and the horizontal axis t represents time. A dotted line 41 represents a transition of the inter-node time difference m1 between the master node 10-1 and the slave node 20 during a predetermined period T0. The long chain line 42 represents the transition of the inter-node time difference m2 between the master node 10-1 and the slave node 20 during a predetermined period T0. An arrow 43 represents the timing at which a series of exchanges related to time synchronization is performed between the master node 10-1 and the slave node 20. That is, the inter-node time difference m1 between the master node 10-1 and the slave node 20 is calculated at the time indicated by the arrow 43. An arrow 44 represents a timing at which a series of exchanges related to time synchronization is performed between the master node 10-2 and the slave node 20. That is, the inter-node time difference m2 between the master node 10-2 and the slave node 20 is calculated at the time indicated by the arrow 44.

In FIG. 12, during a predetermined period T0, a series of exchanges related to time synchronization is performed between the master node 10-1 and the slave node 20 three times, and the master node 10-2 and the slave node 20 are exchanged. It is shown that a series of exchanges related to time synchronization was performed twice.
The slave node 20 calculates the variance value Vk of the inter-node time difference mk based on the inter-node time difference mk calculated at each timing and the period average value Mk in a predetermined period T0.

FIG. 13 is a flowchart showing a process flow of the slave node 20 in the fifth operation example of the present invention. Further, the processing similar to that in FIG. 6 is denoted by the same reference numerals as those in FIG.
When the processing up to step S401 is completed and the predetermined period T0 has elapsed in step S401 (step S401-YES), the calculation unit 205 calculates the period average value based on the time information acquired during the predetermined period T0. Is calculated for each master node 10 (step S1001). The calculation unit 205 calculates a variance value based on the calculated average value for each master node 10 and the inter-node time difference for each series of exchanges related to time synchronization performed during the predetermined period T0. It is calculated every 10 (step S1002). The calculation unit 205 calculates the time difference average value ave4 based on the period average value for each master node 10 and the variance value for each master node 10 (step S1003). The time correction unit 206 corrects the slave time based on the calculated time difference average value ave2 (step S1004).

  According to the slave node 20 configured as described above, even if fluctuation occurs in the delay time between the master node 10 and the slave node 20 due to the influence of queuing delay or the like in the relay device, it is correct. The possibility that the time of the slave node 20 is corrected at a time greatly deviated from the time is reduced. Specifically, a period average value for each master node 10 calculated based on a plurality of pieces of time information respectively acquired with a plurality of master nodes 10 during a predetermined period T0, and a predetermined period T0 A variance value is calculated based on a time difference for each series of exchanges related to time synchronization performed between the two. Then, the slave time is corrected with the average value calculated based on the calculated variance value and the period average value for each master node 10. Therefore, it is possible to improve the possibility of realizing more accurate synchronization. For example, since the accuracy of time to synchronize may be deteriorated due to fluctuations in the network, synchronization with higher accuracy can be realized by incorporating a small fluctuation in the calculation of the time difference average value. Therefore, it is possible to suppress a decrease in accuracy of time synchronization of the slave node 20.

式２３のβｋは、分散値の逆数（１／Ｖｋ）を表す。算出部２０５は、期間平均値Ｍｋの値が小さい順に、分散値の逆数βｋが高い値を順番に重みづけの値として割り当ててもよいし、その他の順番で分散値の逆数βｋを重みづけの値として割り当ててもよい。 <Modification>
In this operation example, the formula (Formula 22) for calculating the time difference average value ave4 when the number of master nodes 10 is two is shown. However, when the number of master nodes 10 is three or more, The calculation unit 205 calculates the time difference average value ave4 based on the following Expression 23.

Βk in Equation 23 represents the reciprocal of the variance value (1 / Vk). The calculation unit 205 may assign values having higher reciprocal values βk as weighting values in order from the smallest average period value Mk, or weight the reciprocal values βk of the distributed values in other orders. It may be assigned as a value.

Instead of the variance value, σk, which is the square root of the variance value, may be used as the weighting value. When configured in this way, the calculation unit 205 calculates the time difference average value ave4 based on the following Expression 24.

  Further, in this operation example, a configuration is shown in which the slave node 20 stores all the time information acquired during the predetermined period T0 and calculates the period average value and the time difference average value ave4 after the predetermined period T0 has elapsed. However, it need not be limited to this. For example, the following processing may be performed. The slave node 20 is a node between the slave node 20 and the master node 10 in which a series of exchanges related to time synchronization are performed after a series of exchanges related to time synchronization is performed for each connected master node 10. The time difference is calculated. The slave node 20 repeatedly executes this process for a predetermined period T0, and calculates the inter-node time difference in the predetermined period T0 for each master node 10. After the elapse of the predetermined period T0, the slave node 20 determines the node based on the inter-node time difference for each master node 10 calculated during the predetermined period T0 and the average period value for each master node in the predetermined period T0. A variance value of the inter-time difference is calculated for each master node. The slave node 20 calculates the time difference average value ave4 based on the variance value calculated for each master node 10 and the period average value for each master node. Hereinafter, a specific example will be described.

When the slave node 20 is connected to a plurality of (for example, two) master nodes 10, the slave node 20 transmits and receives PTP messages to and from each of the plurality of master nodes 10. When the slave node 20 acquires all the time information with the master node 10-1, the slave node 20 determines the inter-node time difference m1 (l between the master node 10-1 and the slave node 20 based on the above equation 12. ) Is calculated.
Similarly, when the slave node 20 acquires all the time information with the master node 10-2, the slave node 20 determines the inter-node time difference between the master node 10-2 and the slave node 20 based on the above equation 13. m2 (l) is calculated.

  Through the processing described above, the slave node 20 calculates the inter-node time difference mk (l) with all the connected master nodes 10 during the predetermined period T0. After a predetermined period T0 has elapsed, the slave node 20 calculates a period average value Mk for each master node 10 based on the inter-node time difference mk (l) calculated during the predetermined period T0. For example, the slave node 20 calculates the period average value M1 of the inter-node time difference m1 (l) between the master node 10-1 and the slave node 20 during the predetermined period T0 based on the above equation 14. Further, for example, the slave node 20 calculates the period average value M2 of the inter-node time difference m2 (l) between the master node 10-2 and the slave node 20 during the predetermined period T0 based on the above formula 15.

  Thereafter, the slave node 20 calculates a variance value Vk of the inter-node time difference based on the inter-node time difference for each master node 10 calculated during the predetermined period T0 and the calculated period average value in the predetermined period T0. Calculate for each master node. Based on the variance value Vk calculated for each master node 10 and the period average value for each master node, the time difference average value ave4 is calculated based on the above equation 22.

  The embodiment of the present invention has been described in detail with reference to the drawings. However, the specific configuration is not limited to this embodiment, and includes designs and the like that do not depart from the gist of the present invention.

10 (10-1 to 10-2) ... Master node, 20 ... Slave node, 30 (30-1 to 30-2) ... Network, 101 ... Master clock generation unit, 102 ... Clock unit, 103 ... Packet generation unit, DESCRIPTION OF SYMBOLS 104 ... Communication part, 201 ... Communication part, 202, ... Control part, 203 ... Synchronization processing part, 204 ... Clock part, 205 ... Calculation part, 206 ... Time correction part

Claims (8)

A communication unit that transmits and receives a control message used for time synchronization processing, which is processing for synchronizing the time in the slave node to the time in the master node, with a plurality of master nodes;
A time correction unit that corrects the time of its own device based on time information acquired when the communication unit transmits and receives the control message;
A slave node comprising A calculation unit that calculates a statistical value of a time difference between the time of each master node and the time of the own device based on the acquired time information;
The slave node according to claim 1, wherein the time correction unit corrects the time of the own device based on the calculated statistical value.   The calculation unit obtains a first statistical value that is a statistical value of a time difference between the time of the master node and the time of the own device in the predetermined period based on the time information acquired during the predetermined period. Based on the calculated first statistical value for each master node, a second statistical value that is a statistical value of a time difference between the time of each master node and the time of the own device is calculated. The slave node according to claim 2. The communication unit further receives the control message including a value indicating the quality of the time source of each master node during the time synchronization process,
The calculation unit calculates a time difference between the time of the master node and the time of the own device based on the acquired time information for each master node, and receives the calculated time difference for each master node. The slave node according to claim 2, wherein the statistical value is calculated based on the time difference for each weighted master node after weighting with a value representing the quality of the time source included in the control message. . The communication unit further receives the control message including a value indicating the quality of the time source of each master node during the time synchronization process,
The calculation unit obtains a first statistical value that is a statistical value of a time difference between the time of the master node and the time of the own device in the predetermined period based on the time information acquired during the predetermined period. The first statistical value calculated for each master node is weighted with a value representing the quality of the time source included in the received control message, and then the weighted first statistics value is calculated for each master node. The slave node according to claim 2, wherein a second statistical value that is a statistical value of a time difference between the time of each master node and the time of its own device is calculated based on the statistical value of 1.   The calculation unit obtains a first statistical value that is a statistical value of a time difference between the time of the master node and the time of the own device in the predetermined period based on the time information acquired during the predetermined period. The first statistic calculated for each master node and weighted with the variance value of the time difference for each master node in a predetermined period for the calculated first statistic value for each master node. The slave node according to claim 2, wherein a second statistical value, which is a statistical value of a time difference between the time of each master node and the time of its own device, is calculated based on the value. A communication step of transmitting and receiving a control message used for time synchronization processing, which is processing for synchronizing the time at the slave node to the time at the master node, with a plurality of master nodes;
A time correction step of correcting the time of the slave node based on time information acquired when the control message is transmitted and received by the communication step;
A time synchronization method. A communication step of transmitting and receiving a control message used for time synchronization processing, which is processing for synchronizing the time at the slave node to the time at the master node, with a plurality of master nodes;
A time correction step of correcting the time of the slave node based on time information acquired when the control message is transmitted and received by the communication step;
A computer program for causing a computer to execute.

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