JP5515735B2 - Time synchronization system, master node, slave node, relay device, time synchronization method, and time synchronization program - Google Patents

Description

  The present invention relates to a technique for synchronizing time between nodes that perform communication.

  Conventionally, high-accuracy time synchronization is required for mobile backhaul, factory automation, home AV LAN (Local Area Network), and the like. Against this background, standardization of technology for performing time synchronization is underway. For example, there is IEEE 1588 as a technique for performing time synchronization with accuracy of less than microseconds in a packet network (see Non-Patent Document 1).

  In the technology defined in IEEE1588, time stamp information is exchanged by exchanging messages between master / slave nodes. The slave node calculates a time lag (Offset) of the slave node with respect to the master node from the message transmission / reception times at the master and the slave node. Then, the slave node corrects the time of the slave node based on this Offset, and synchronizes the time of the slave node with the master node.

  In IEEE1588, in order to obtain Offset, it is assumed that the transmission delay (MS_Delay) from the master node to the slave node is equal to the transmission delay (SM_Delay) from the slave node to the master node. However, in packet networks, MS_Delay and SM_Delay are likely to be different values due to queuing delays in relay nodes such as routers and switches. For this reason, the assumption that MS_Delay and SM_Delay are equal causes an error in Offset, which degrades the time synchronization accuracy.

  In order to solve such a problem, IEEE 1588 version 2 defines a Transparent Clock (TC) function. In the following description, IEEE 1588 using the TC function is referred to as IEEE 1588v2 w / TC.

IEEE P1588 TM / D1, “Draft Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems”, June, 2007.

However, in IEEE1588v2 w / TC, in order to achieve high accuracy, more relay nodes (ultimately all relay nodes) need to have a TC function. On the other hand, most existing nodes already placed in the network do not have the TC function. Therefore, in order to realize IEEE1588v2 w / TC, it is necessary to replace the relay node and add functions. Therefore, there is a problem that the realization of IEEE1588v2 w / TC is very difficult from the viewpoint of cost and labor.
In view of the above circumstances, it is an object of the present invention to provide a technique for reducing the cost required for introduction and realizing highly accurate time synchronization.

  One aspect of the present invention includes a master node and a slave node that communicate with each other, and a relay device that relays communication between the master node and the slave node, and synchronizes the time at the slave node with the time at the master node. The master node includes a transmission unit that transmits a control message to the slave node, and a reception unit that receives a control message from the slave node, and the master node or the relay device includes the slave A first delay measuring unit for measuring a first delay amount representing a queuing delay received in a communication path by a control message transmitted from a node to the master node; and the first delay measured by the first delay measuring unit. A notification unit for notifying the slave node of the amount, Alternatively, the relay device includes a second delay measuring unit that measures a second delay amount indicating a queuing delay received in a communication path by a control message transmitted from the master node to the slave node, A transmission unit that transmits a control message to the master node, a reception unit that receives the control message from the master node, the first delay amount notified from the master node, and the second delay measurement unit. A time synchronization control unit that calculates a difference between the time at the slave node and the time at the master node using the measured second delay amount, and synchronizes the time at the slave node with the time at the master node; It is characterized by providing.

  One aspect of the present invention is a transmitter that communicates with a master node and transmits a control message to the master node; a receiver that receives a control message from the master node; and the control message transmitted from the master node A second delay measuring unit that measures a second delay amount representing a queuing delay received in the communication path, the first delay amount notified from the master node, and the second delay measuring unit measured by the second delay measuring unit And a time synchronization control unit that synchronizes the time with the time in the master node using a second delay amount, and is a master node provided in a time synchronization system having a slave node, and controls the slave node A transmitter for transmitting a message, a receiver for receiving a control message from the slave node, and the slave node A first delay measuring unit for measuring a first delay amount representing a queuing delay received in a communication path from a control message transmitted from the master node to the master node, and the first delay amount measured by the first delay measuring unit And a notification unit for notifying the slave node.

  One aspect of the present invention is a transmitter that communicates with a slave node and transmits a control message to the slave node; a receiver that receives a control message from the slave node; and a control message transmitted from the slave node. A master node comprising: a first delay measurement unit that measures a first delay amount that represents a queuing delay received in a communication path; and a notification unit that notifies the first delay amount measured by the first delay measurement unit A slave node provided in a time synchronization system having a transmitter that transmits a control message to the master node, a receiver that receives the control message from the master node, and a slave node from the master node A second delay that represents the queuing delay that the control message sent to Using the second delay measuring unit that measures the amount, the first delay amount notified from the master node, and the second delay amount measured by the second delay measuring unit of the device itself, the slave A time synchronization control unit that calculates a difference between the time at the node and the time at the master node and synchronizes the time at the slave node with the time at the master node.

  One aspect of the present invention is a relay device that relays communication between a master node and a slave node that synchronizes the time with the time of the master node, the control being transmitted from the slave node to the master node A first delay measurement unit that measures a first delay amount that represents a queuing delay that the message has received in the communication path, and a control message that is transmitted from the master node to the slave node represents the queuing delay that has been received in the communication path A second delay amount is measured, and the difference between the time at the slave node and the time at the master node is calculated using the first delay amount and the measured second delay amount; The first delay measuring unit measures the slave node that synchronizes the time with the time in the master node. Comprising a notification unit, a notifying said first delay amount which is.

  One aspect of the present invention is a relay device that relays communication between a master node and a slave node that synchronizes time with the time of the master node, the control being transmitted from the master node to the slave node A second delay measuring unit that measures a second delay amount that represents a queuing delay that the message has received in the communication path; and a control message that is transmitted from the slave node to the master node represents the queuing delay that has been received in the communication path. The slave that calculates the difference between the time at the slave node and the time at the master node by using the first delay amount and the second delay amount, and synchronizes the time at the slave node with the time at the master node The node that notifies the second delay amount measured by the second delay measurement unit to the node. It comprises a part, a.

  One aspect of the present invention includes a master node and a slave node that communicate with each other, and a relay device that relays communication between the master node and the slave node, and synchronizes the time at the slave node with the time at the master node. The master node transmits a control message to the slave node, the master node receives a control message from the slave node, and the master node or A first delay measuring step in which the relay device measures a first delay amount representing a queuing delay received in a communication path by a control message transmitted from the slave node to the master node; and the master node or the relay device. Is determined by the first delay measurement step. A notification step of notifying the slave node of the measured first delay amount, a transmission step of the slave node transmitting a control message to the master node, and the slave node from the master node to the control message And a second delay in which the slave node or the relay device measures a second delay amount representing a queuing delay received in a communication path by a control message transmitted from the master node to the slave node. The measurement step, the slave node using the first delay amount notified from the master node and the second delay amount measured by the second delay measurement step, the time at the slave node and the The difference with the time at the master node is calculated, and the slave node Characterized in that it comprises a time synchronization control step of synchronizing the time to time in the master node, the at.

  One aspect of the present invention includes a master node and a slave node that communicate with each other, and a relay device that relays communication between the master node and the slave node, and synchronizes the time at the slave node with the time at the master node. A time synchronization program for operating a first computer corresponding to the master node, a second computer corresponding to the slave node, and a third computer corresponding to the relay device, One computer is caused to execute a transmission step of transmitting a control message to the slave node and a reception step of receiving a control message from the slave node, to the first computer or the third computer , From the slave node to the master A first delay measurement step of measuring a first delay amount representing a queuing delay received in a communication path by a control message transmitted to a communication path, and the first delay amount measured by the first delay measurement step A notification step of notifying a slave node, and causing the second computer or the third computer to receive a queuing delay received in a communication path by a control message transmitted from the master node to the slave node. A second delay measuring step of measuring a second delay amount to be expressed, a transmission step of transmitting a control message to the master node to the second computer, and receiving the control message from the master node A receiving step, the first delay amount notified from the master node, and the first delay amount. A time for calculating a difference between the time at the slave node and the time at the master node using the second delay amount measured by the delay measurement step, and synchronizing the time at the slave node with the time at the master node And a synchronization control step.

  According to the present invention, it is possible to reduce the cost required for introduction and realize highly accurate time synchronization.

FIG. 3 is a sequence diagram showing a communication sequence by an IEEE 1588 time synchronization algorithm. It is the schematic showing the outline of the time synchronization algorithm of IEEE1588 and IEEE1588v2 w / TC. It is a system configuration figure of the communications system in a 1st embodiment. It is a functional block diagram showing the functional structure of a master node. It is a functional block diagram showing the detailed functional structure of a delay measurement part. It is the schematic showing the outline | summary of operation | movement of a packet counter. It is a functional block diagram showing the functional structure of a slave node. It is a functional block diagram showing the detailed functional structure of a delay measurement part. It is a functional block diagram showing the detailed functional structure of a time synchronous control part. It is a flowchart showing the flow of the master 1st process by a master node. It is a flowchart showing the flow of the slave 1st process by a slave node. It is a flowchart showing the flow of the master 2nd process by a master node. It is a flowchart showing the flow of the slave 2nd process by a slave node. It is a sequence diagram showing the specific example of the time synchronous process by a communication system. It is a sequence diagram showing the specific example of the time synchronous process by a communication system. It is a figure showing the probability distribution of the delay amount measured in a communication system. It is a figure showing the outline of a process of a delay measurement part at the time of comprising using a packet buffer. It is a functional block diagram showing the functional structure of the master node in 2nd Embodiment. It is a functional block diagram showing the functional structure of the slave node in 2nd Embodiment. It is a functional block diagram showing the functional structure of the time synchronous control part in 2nd Embodiment. It is a flowchart showing the flow of the master 2nd process in 2nd Embodiment. It is a flowchart showing the flow of the slave 2nd process in 2nd Embodiment. It is a sequence diagram showing the specific example of the time synchronous process by the communication system in 2nd Embodiment. It is a system configuration figure of the communications system in a 3rd embodiment. It is a functional block diagram showing the functional structure of the master node in 3rd Embodiment. It is a functional block diagram showing the functional structure of the slave node in 3rd Embodiment. It is a functional block diagram showing the detailed functional structure of a time synchronous control part. It is a functional block diagram showing the functional structure of the emulation node in 3rd Embodiment. It is a flowchart showing the flow of the slave 1st process in 3rd Embodiment. It is a flowchart showing the flow of the master 2nd process in 3rd Embodiment. It is a flowchart showing the flow of the slave 2nd process in 3rd Embodiment. It is a flowchart showing the flow of the process by the emulation node in 3rd Embodiment. It is a sequence diagram showing the specific example of the time synchronous process by the communication system in 3rd Embodiment.

[IEEE1588]
First, the IEEE 1588 time synchronization algorithm will be described. FIG. 1 is a sequence diagram showing a communication sequence according to the IEEE 1588 time synchronization algorithm. In FIG. 1, the master node 100 and the slave node 200 perform bidirectional communication, and the slave node 200 periodically synchronizes the time with the master node 100.

  The master node 100 periodically transmits a Sync message to the slave node 200 (step S100). The master node 100 records the transmission time (hereinafter referred to as “Sync transmission time”) Tm (0) of this Sync message (step S101). Next, the master node 100 transmits a Follow_up message to the slave node 200. At this time, the master node 100 stores the Sync transmission time Tm (0) in the Follow_up message.

  Upon receiving the Sync message, the slave node 200 records the reception time of the Sync message (hereinafter referred to as “Sync reception time”) Ts (0) using this reception process as a trigger (step S102). Next, the slave node 200 receives the Follow_up message and extracts and records the Sync transmission time Tm (0) stored in the Follow_up message. Next, the slave node 200 transmits a Delay_Request message to the master node 100 (step S104). Then, the slave node 200 records the transmission time of this Delay_Request message (hereinafter referred to as “Delay transmission time”) Ts (1) (step S105).

  When receiving the Delay_Request message, the master node 100 records the reception time of the Delay_Request message (hereinafter referred to as “Delay reception time”) Tm (1) using this reception process as a trigger (step S106). Next, the master node 100 transmits a Delay_Response message to the slave node 200 (step S107). At this time, the master node 100 stores the Delay reception time Tm (1) in the Delay_Response message.

When the slave node 200 receives the Delay_Response message, the slave node 200 extracts and records the Delay reception time Tm (1) stored in the Delay_Response message.
Based on the Sync transmission time Tm (0) and the Sync reception time Ts (0), the slave node 200 calculates the time at the master node 100 (hereinafter referred to as “master time”) and the slave node 200 from the following Expression 1. The difference MS_Diff from the time (hereinafter referred to as “slave time”) is calculated.
MS_Diff = Ts (0)-Tm (0) = MS_Delay + Offset ・ ・ ・ Equation 1

In addition, the slave node 200 obtains a difference between the slave time and the master time from the following formula 2 based on the Delay transmission time Ts (1) and the Delay reception time Tm (1).
SM_Diff = Tm (1)-Ts (1) = SM_Delay-Offset ・ ・ ・ Equation 2

  Here, MS_Delay represents a transmission delay from the master node 100 to the slave node 200, SM_Delay represents a transmission delay from the slave node 200 to the master node 100, and Offset represents a time offset (advance) of the slave node 200 with respect to the master node 100. Represents. The transmission delays MS_Delay and SM_Delay are composed of a propagation delay between the master node 100 and the slave node 200 and a queuing delay that occurs at a relay node on the network between the master node 100 and the slave node 200.

  As described above, two expressions, Expression 1 and Expression 2, are obtained with respect to Offset, which is a time lag of the slave node 200 with respect to the master node 100. However, these two equations include unknown parameters MS_Delay and SM_Delay in addition to Offset. Therefore, since there are only two equations for the three unknown parameters, Offset cannot be calculated. Therefore, in IEEE1588, assuming that the transmission delay MS_Delay from the master node 100 to the slave node 200 is equal to the transmission delay SM_Delay from the slave node 200 to the master node 100, and that both values are delays, 1 and 2 are transformed into the following equations 3 and 4.

MS_Diff = Delay + Offset ・ ・ ・ Equation 3
SM_Diff = Delay-Offset ・ ・ ・ Equation 4
By solving the simultaneous equations of Equation 3 and Equation 4, the following Equation 5 is derived.
Offset = (MS_Diff-SM_Diff) / 2 ... Formula 5

  The slave node 200 calculates Offset based on Equation 5, and corrects the slave time based on Offset to synchronize the slave time with the master time. The above is the time synchronization algorithm defined in IEEE1588.

[IEEE1588v2 w / TC]
Next, the IEEE 1588v2 w / TC time synchronization algorithm will be described. FIG. 2 is a schematic diagram showing an outline of the time synchronization algorithm of IEEE1588 and IEEE1588v2 w / TC. FIG. 2A shows an outline of the IEEE 1588 time synchronization algorithm. FIG. 2B shows an outline of the IEEE 1588v2 w / TC time synchronization algorithm. D1 to D6 in FIGS. 2A and 2B represent queuing delays in transmission in the direction of the arrow, which occur in the relay nodes Re1 to Re3, respectively.

  In IEEE1588v2 w / TC, each relay node Re1 to Re3 has a TC function. The TC function is a function that measures the stay time in the node of the packet of the control message (IEEE 1588 message), writes the time in a predetermined field of the control packet, and cumulatively adds it. Note that the IEEE 1588 message is specifically a Sync message and a Delay_Request message. In IEEE1588v2 w / TC, the stay time at the relay nodes Re1 to Re3 is cumulatively added to the message every time the control packet passes through the relay nodes Re1 to Re3 by the TC function. Therefore, the slave node 200 can accurately acquire the sum of the queuing delays that have occurred in the relay nodes Re1 to Re3 in the transmission from the master node 100 to the slave node 200. Similarly, the master node 100 can accurately obtain the sum of the queuing delays that occurred in the relay nodes Re1 to Re3 in the transmission from the slave node 200 to the master node 100.

The total queuing delay and propagation delay in transmission from the master node 100 to the slave node 200 are MS_Q and MS_P, respectively, and the total queuing delay and propagation delay in transmission from the slave node 200 to the master node 100 are SM_Q, respectively. , SM_P, Equation 1 and Equation 2 described above can be transformed into Equation 6 and Equation 7 below.
MS_Diff = MS_P + MS_Q + Offset ・ ・ ・ Formula 6
SM_Diff = SM_P + SM_Q-Offset ・ ・ ・ Equation 7

Here, when the message transmission path of the transmission from the master node 100 to the slave node 200 and the transmission from the slave node 200 to the master node 100 are equal in both directions, MS_P = SM_P = Propagation_Delay. In this case, Equation 6 and Equation 7 can be transformed as Equation 8 and Equation 9 below.
MS_Diff = Propagation_Delay + MS_Q + Offset ・ ・ ・ Formula 8
SM_Diff = Propagation_Delay + SM_Q-Offset ・ ・ ・ Equation 9

Then, from Expression 8 and Expression 9, the following Expression 10 can be obtained as an expression for calculating Offset.
Offset = {(MS_Diff-SM_Diff)-(MS_Q-SM_Q)} / 2 Equation 10

  As shown in FIG. 2A, IEEE1588 (hereinafter also referred to as “Pure IEEE1588”), which is not IEEE1588v2 w / TC, assumes that the sum of queuing delays occurring in each relay node Re1 to Re3 is equal in both directions. It was. That is, the total queuing delay in transmission from the master node 100 to the slave node 200 (D1 + D2 + D3) and the total queuing delay in transmission from the slave node 200 to the master node 100 (D4 + D5 + D6) Was assumed to be equal. However, since they are not actually equal, the error has caused the deterioration of synchronization accuracy.

  On the other hand, in IEEE1588v2 w / TC, the total of queuing delays at each relay node Re1 to Re3 is measured by the TC function implemented at each relay node Re1 to Re3. Then, the slave node 200 accurately acquires the total value (D1 + D2 + D3) of the queuing delay in the transmission from the master node 100 to the slave node 200. Further, the master node 100 accurately acquires the total value (D4 + D5 + D6) of the queuing delay in the transmission from the slave node 200 to the master node 100. With such an operation, IEEE 1588v2 w / TC enables highly accurate time synchronization. The above is the time synchronization algorithm defined in IEEE1588v2 w / TC.

[First Embodiment]
FIG. 3 is a system configuration diagram of the communication system 1 in the first embodiment. The communication system 1 includes a master node 300, slave nodes 400 (400a to 400c), and a packet network PN. Hereinafter, details of the configurations of the master node 300 and the slave node 400 will be described.

[Master node]
FIG. 4 is a functional block diagram showing the functional configuration of the master node 300. The master node 300 includes a clock generation unit 301, a master clock unit 302, a packet generation unit 303, a packet transmission unit 304, a packet reception unit 305, and a delay measurement unit 306. The master node 300 includes, for example, a CPU (Central Processing Unit) connected via a bus, a memory, an auxiliary storage device, a communication interface, and the like, and is configured as a device including each of the above functional units by executing a time synchronization program. Also good.

  The clock generation unit 301 generates a reference clock for the master node 300. Specifically, the clock generation unit 301 determines a time width of 1 second in the master node 300. Note that the clock generation unit 301 may exist outside the master node 300. In this case, the master node 300 is configured to reliably acquire a clock from the clock generation unit 301 installed outside.

  The master clock unit 302 determines the time (master time) of the master node 300 according to the reference clock generated by the clock generation unit 301. Specifically, the master clock unit 302 determines what hours, minutes, and seconds in the master node 300.

  The packet generation unit 303 generates an IEEE 1588 message and sends it to the packet transmission unit 304. Specifically, the IEEE 1588 message includes a Sync message, a Follow_up message, and a Delay_Response message. The packet generation unit 303 periodically transmits a Sync message to the slave node 400 via the packet transmission unit 304, and simultaneously records the Sync transmission time Tm (0) with reference to the master clock unit 302. Further, after transmitting the Sync message, the packet generation unit 303 generates a Follow_up message storing the Sync transmission time Tm (0), and transmits it to the slave node 400 via the packet transmission unit 304. Also, the packet generation unit 303 receives the Delay_Request message reception time (Delay reception time) Tm (1) received by the packet reception unit 305, and the delay amount SM_Q (first delay amount) of the Delay_Request message measured by the delay measurement unit 306. ) Is stored and transmitted to the slave node 400 via the packet transmission unit 304. Note that the delay amount SM_Q represents the delay amount of the queuing delay received while the Delay_Request message is transferred from each slave node 400a to 400c to the master node 300 as described above.

  The Delay_Response message is a reply to the Delay_Request message transmitted from the slave nodes 400a to 400c. Therefore, the packet generation unit 303 manages the Delay reception time Tm (1) and the delay amount SM_Q stored in the Delay_Response message for each slave node 400a to 400c that is the source of the Delay_Request message.

  The packet transmission unit 304 transmits the Sync message, Follow_up message, and Delay_Response message received from the packet generation unit 303 to the slave nodes 400a to 400c via the packet network PN. The packet transmission unit 304 broadcasts a Sync message and Follow_up message to the slave nodes 400a to 400c. The packet transmission unit 304 unicasts the Delay_Response message to the slave nodes 400a to 400c that are the transmission sources of the Delay_Request messages.

  The packet receiving unit 305 receives a Delay_Request message sent from the slave nodes 400a to 400c via the packet network PN. Then, the packet reception unit 305 transfers the received Delay_Request message to the packet generation unit 303 and the delay measurement unit 306.

  The delay measurement unit 306 includes a packet counter. The delay measuring unit 306 calculates the delay amount SM_Q of the arriving Delay_Request message by monitoring the increase / decrease state of the counter value of the packet counter. Then, the delay measurement unit 306 notifies the packet generation unit 303 of the calculated delay amount SM_Q.

  FIG. 5 is a functional block diagram illustrating a detailed functional configuration of the delay measurement unit 306. The delay measurement unit 306 includes a packet counter 501, a counter maximum value monitor unit 502, an arrival counter value monitor unit 503, and a delay calculation unit 504. The counter maximum value monitoring unit 502 and the arrival time counter value monitoring unit 503 monitor the counter value of the packet counter 501 and notify the delay calculation unit 504 of the result. The delay calculation unit 504 calculates the delay amount SM_Q using information notified from the counter maximum value monitor unit 502 and the arrival time counter value monitor unit 503. Then, the delay calculation unit 504 notifies the packet generation unit 303 of the calculated delay amount SM_Q.

  Each time the packet counter 501 receives a Delay_Request message from the packet receiver 305, the packet counter 501 increases the counter value by a predetermined value. Further, the packet counter 501 decreases the counter value according to the frequency of the reference clock output from the clock generation unit 301. The counter value of the packet counter 501 decreases according to the frequency of the reference clock because the packet of the Delay_Request message received by the packet receiving unit 305 is read from the buffer of the received packet according to the frequency of the reference clock.

  The counter maximum value monitor unit 502 detects the maximum value of the counter value of the packet counter 501. Specifically, the counter maximum value monitoring unit 502 detects the maximum value within a monitoring period of a predetermined time (for example, 10 seconds). Hereinafter, the maximum value of the counter in the monitoring period i is expressed as a counter maximum value P (i). When the monitoring period i ends, the counter maximum value monitoring unit 502 notifies the delay calculating unit 504 of the counter maximum value P (i) that is the detection result.

  Upon arrival, the counter value monitor unit 503 detects the counter value C (i, n) upon arrival when the n-th Delay_Request message packet arrives in the monitoring period i. The arrival time counter value monitoring unit 503 detects the counter value C (i, n) every time the Delay_Request message packet arrives, and notifies the delay calculation unit 504 of the detection result.

The delay calculation unit 504 uses the counter value C (i, n) and the counter maximum value P (i) each time the counter value C (i, n) is received from the arrival counter value monitoring unit 503, and the following equation is obtained. 11 is used to calculate the delay amount SM_Q.
SM_Q = P (i-1)-C (i, n) Equation 11
The delay calculation unit 504 notifies the packet generation unit 303 of the delay amount SM_Q every time the delay amount SM_Q is calculated.

  FIG. 6 is a schematic diagram showing an outline of the operation of the packet counter 501. In FIG. 6, the vertical axis represents the counter value, and represents a high counter value from the bottom to the top. The horizontal axis represents time and progresses from left to right. A plurality of broken lines arranged at equal intervals in the vertical direction represent the timing at which a packet of a Delay_Request message is received when no queuing delay occurs. The arrow pointing upward indicates the timing when the packet of the Delay_Request message is actually received. When receiving the Delay_Request message packet, the packet counter 501 increases the counter value by a fixed value (CV in FIG. 6). When the vertically extending broken line and the upward arrow coincide with each other on the time axis, that is, when a Delay_Request message packet is received without causing a queuing delay, the counter value takes the maximum value Cmax. In this case, the packet counter 501 matches the total number of received bits with the total number of bits read periodically according to the frequency of the reference clock. On the other hand, when a queuing delay occurs, the counter value is smaller than Cmax. At this time, the difference between the maximum value Cmax and the counter value is equivalent to the delay amount of the generated queuing delay.

[Slave node]
FIG. 7 is a functional block diagram illustrating a functional configuration of the slave node 400. Note that each of the slave nodes 400 a to 400 c has the same configuration as that of the slave node 400. The slave node 400 includes a packet reception unit 401, a PLL (Phase Locked Loop) unit 402, a delay measurement unit 403, a slave clock unit 404, a time synchronization control unit 405, and a packet transmission unit 406. The slave node 400 may include, for example, a CPU, a memory, an auxiliary storage device, a communication interface, and the like connected by a bus, and may be configured as a device including the above-described functional units by executing a time synchronization program.

  The packet receiving unit 401 receives the Sync message, Follow_up message, and Delay_Request message transmitted from the master node 300 via the packet network PN, and transfers them to the time synchronization control unit 405. The packet reception unit 401 transfers only the Sync message to the PLL unit 402 and the delay measurement unit 403.

  The PLL unit 402 includes a phase comparator 407, an LPF (Low Pass Filter) 408, a PI (Proportional Integral) controller 409, a VCO (voltage controlled oscillator) 410, and a counter 411. However, such a configuration of the PLL unit 402 is merely an example. That is, the PLL unit 402 can calculate a difference between a TS (Time Stamp) generated from its own clock and a TS received from the master node 300, and adjust its own clock based on the difference. Any other configuration may be used.

  The phase comparator 407 calculates a difference signal between the reception time stamp stored in the Sync message packet received from the packet reception unit 401 and the time stamp generated by the counter 411. Then, the phase comparator 407 outputs a differential signal representing the calculation result to the LPF 408.

The LPF 408 levels the difference signal output by the phase comparator 407, suppresses jitter and noise, and outputs the result to the PI controller 409.
The PI controller 409 generates a control signal such that the leveled difference signal finally becomes zero and outputs it to the VCO 410.

The VCO 410 generates a clock having a frequency determined by the control signal output from the PI controller 409 and outputs the clock to the counter 411. In addition, the VCO 410 decreases the counter value of the packet counter of the delay measurement unit 403 according to the generated frequency clock.
The counter 411 generates a time stamp based on the clock generated by the VCO 410 and transfers the time stamp to the phase comparator 407.

With the operation of the PLL unit 402 described above, the clock of the slave node 400 generated by the VCO 410 is synchronized with the clock of the master node 300.
The delay measurement unit 403 includes a packet counter. The delay measurement unit 403 calculates the delay amount MS_Q (second delay amount) of the incoming Sync message by monitoring the increase / decrease state of the counter value of the packet counter. Then, the delay measurement unit 403 notifies the time synchronization control unit 405 of the calculated delay amount MS_Q. Note that the delay amount MS_Q represents the delay amount of the queuing delay received while the Sync message is transferred from the master node 300 to the slave node 400 as described above.

  FIG. 8 is a functional block diagram illustrating a detailed functional configuration of the delay measurement unit 403. The delay measurement unit 403 includes a packet counter 601, a counter maximum value monitor unit 602, an arrival counter value monitor unit 603, and a delay calculation unit 604. Each configuration provided in the delay measurement unit 403 is the same as each configuration having the same name provided in the delay measurement unit 306 of the master node 300. However, each time the packet counter 601 receives a Sync message from the packet receiver 401, the packet counter 601 increases the counter value by a predetermined value. Further, the packet counter 601 decreases the counter value in accordance with the frequency of the clock output by the VCO 410. Further, the delay calculation unit 604 calculates the delay amount MS_Q by the same process instead of the delay amount SM_Q, and notifies the time synchronization control unit 405 of the calculated delay amount MS_Q.

  Returning to FIG. 7, the description of the configuration of the slave node 400 will be continued. The slave clock unit 404 determines the time (slave time) of the slave nodes 400a to 400c according to the clock generated by the VCO 410.

The time synchronization control unit 405 transmits and receives Sync message and Delay_Request message transmission / reception time information (Sync transmission time Tm (0), Sync reception time Ts (0), Delay transmission time Ts (1), Delay reception time Tm (1)), Using the delay amount SM_Q and the delay amount MS_Q, an offset that is a time lag of the slave node 400 with respect to the master node 300 is obtained. Then, the time synchronization control unit 405 corrects the time of the slave clock unit 404 (slave time). Also, the time synchronization control unit 405 generates a Delay_Request message and sends it to the packet transmission unit 406.
The packet transmission unit 406 transmits the Delay_Request message received from the time synchronization control unit 405 to the master node 300 via the packet network PN.

FIG. 9 is a functional block diagram illustrating a detailed functional configuration of the time synchronization control unit 405. The time synchronization control unit 405 includes a packet analysis unit 701, a packet generation unit 702, an offset calculation unit 703, and a time adjustment unit 704.
The packet analysis unit 701 receives a Sync message, Follow_up message, and Delay_Response message from the packet reception unit 401. When receiving the Sync message, the packet analysis unit 701 refers to the slave clock unit 404 and acquires the Sync reception time Ts (0). The packet analysis unit 701 notifies the offset calculation unit 703 of the acquired Sync reception time Ts (0).

  Further, when receiving the Follow_up message, the packet analysis unit 701 extracts the Sync transmission time Tm (0) stored in the Follow_up message. Then, the packet analysis unit 701 notifies the extracted Sync transmission time Tm (0) to the offset calculation unit 703 and sends a generation trigger of a Delay_Request message to the packet generation unit 702.

  Further, when receiving the Delay_Response message, the packet analysis unit 701 extracts the Delay reception time Tm (1) and the delay amount SM_Q stored in the Delay_Response message, and notifies the offset calculation unit 703 of them.

  The packet generator 702 generates a Delay_Request message. Specifically, upon receiving a Delay_Request message generation trigger from the packet analysis unit 701, the packet generation unit 702 generates a Delay_Request message. The packet generation unit 702 transfers the generated Delay_Request message to the packet transmission unit 406 and refers to the slave clock unit 404 to acquire the Delay transmission time Ts (1). Then, the packet generation unit 702 notifies the obtained delay transmission time Ts (1) to the offset calculation unit 703.

  The offset calculation unit 703 calculates Offset and notifies the time adjustment unit 704 of the calculated Offset. Specifically, each time received from the packet analysis unit 701 and the packet generation unit 702 (Sync transmission time Tm (0), Sync reception time Ts (0), Delay transmission time Ts (1), Delay reception time Tm (1) )), The delay amount SM_Q received from the packet analysis unit 701, and the delay amount MS_Q received from the delay measurement unit 403, the offset is calculated.

  The time adjustment unit 704 adjusts the slave time of the slave clock unit 404 using Offset notified from the offset calculation unit 703. By this processing of the time adjustment unit 704, the slave time of the slave clock unit 404 is synchronized with the master time of the master clock unit 302 of the master node 300.

[Operation]
Next, the flow of processing of each device of the communication system 1 in the first embodiment will be described. In the communication system 1, as processing for time synchronization, master first processing by the master node 300, slave first processing by the slave node 400, master second processing by the master node 300, slave second processing by the slave node 400, Each is executed in this order. 10 and 12 are flowcharts showing the flow of the master first process and the master second process by the master node 300, respectively. 11 and 13 are flowcharts showing the flow of the slave first process and the slave second process by the slave node 400, respectively. The slave nodes 400a to 400c individually execute the first slave process and the second slave process illustrated in FIGS. 11 and 13.

  First, the master first process by the master node 300 will be described with reference to FIG. First, the master node 300 transmits a Sync message to the slave node 400 (step S201). Specifically, the packet generation unit 303 generates a Sync message, and the packet transmission unit 304 broadcasts the Sync message to the slave nodes 400 (400a to 400c). Next, the master node 300 records the Sync transmission time Tm (0) (step S202). Specifically, the packet generation unit 303 refers to the master clock unit 302 to acquire and hold the Sync transmission time Tm (0). Then, the master node 300 transmits a Follow_up message to the slave node 400 (step S203). Specifically, the packet generation unit 303 generates a Follow_up message storing the Sync transmission time Tm (0), and the packet transmission unit 304 broadcast-transmits the Follow_up message to the slave nodes 400 (400a to 400c). The master node 300 periodically repeats the master first process.

  Next, the slave first process by the slave node 400 will be described with reference to FIG. First, the slave node 400 receives a Sync message from the master node 300 (step S301). Specifically, the packet reception unit 401 receives a Sync message from the master node 300 and transfers the received Sync message to the PLL unit 402, the delay measurement unit 403, and the time synchronization control unit 405. In the operation after receiving the Sync message, the processes in steps S302 to S306 and the processes in steps S307 and S308 are executed in parallel.

  First, the processing of steps S302 to S306 will be described. First, the slave node 400 records the Sync reception time Ts (0) (step S302). Specifically, the packet analysis unit 701 of the time synchronization control unit 405 acquires the Sync reception time Ts (0) by referring to the slave clock unit 404 in response to the reception of the Sync message, and notifies the offset calculation unit 703 To do.

  Next, the slave node 400 receives a Follow_up message from the master node 300 (step S303). Specifically, the packet reception unit 401 receives a Follow_up message from the master node 300 and transfers the received Follow_up message to the time synchronization control unit 405. Next, the slave node 400 records the Sync transmission time Tm (0) (step S304). Specifically, the packet analysis unit 701 of the time synchronization control unit 405 extracts and acquires the Sync transmission time Tm (0) stored in the payload part of the Follow_up message in response to reception of the Follow_up message. Then, the packet analysis unit 701 notifies the obtained Sync transmission time Tm (0) to the offset calculation unit 703.

  Next, the slave node 400 transmits a Delay_Request message to the master node 300 (step S305). Specifically, the packet analysis unit 701 sends a Delay_Request message generation trigger to the packet generation unit 702. The packet generation unit 702 generates a Delay_Request message according to the generation trigger, and transfers it to the packet transmission unit 406. Then, the packet transmission unit 406 transmits a Delay_Request message to the master node 300. At this time, the slave node 400 records the Delay transmission time Ts (1) (step S306). Specifically, the packet generation unit 702 refers to the slave clock unit 404, acquires the Delay transmission time Ts (1), and transfers it to the offset calculation unit 703.

  Next, the processing of steps S307 and S308 will be described. First, the slave node 400 measures the delay amount MS_Q (step S307). Specifically, the counter maximum value monitoring unit 502 and the arrival time counter value monitoring unit 503 of the delay measurement unit 403 monitor the counter value of the packet counter 501, respectively, and the maximum counter value during the interval period and the counter when each Sync message arrives. Get the value. Then, the delay calculation unit 504 of the delay measurement unit 403 calculates the delay amount MS_Q based on both counter values.

  Next, the slave node 400 records the measured delay amount MS_Q (step S308). Specifically, the delay calculation unit 504 notifies the calculated delay amount MS_Q to the offset calculation unit 703 of the time synchronization control unit 405.

  Next, the master second process by the master node 300 will be described with reference to FIG. First, the master node 300 receives a Delay_Request message from the slave node 400 (step S401). Specifically, the packet reception unit 305 receives a Delay_Request message from the slave node 400 and transfers the received Delay_Request message to the packet generation unit 303 and the delay measurement unit 306.

  Next, the master node 300 records the delay reception time Tm (1) (step S402). Specifically, the packet generation unit 303 refers to the master clock unit 302 in response to receiving the Delay_Request message, and acquires the time Tm (1) at the time of receiving the Delay_Request message. Then, the packet generation unit 303 records the Delay reception time Tm (1) of each Delay_Request message in association with the node information of the slave nodes 400a to 400c that is the transmission source of each Delay_Request message.

  Next, the master node 300 measures the delay amount SM_Q for each Delay_Request message (step S403). Specifically, the counter maximum value monitoring unit 502 and the arrival time counter value monitoring unit 503 of the delay measurement unit 306 monitor the counter value of the packet counter 501, and each of the maximum counter value in the interval period and the time when each Delay_Request message arrives. Get the counter value. Next, the delay calculation unit 504 calculates the delay amount SM_Q of each Delay_Request message based on both counter value information. Then, the delay measurement unit 306 notifies the packet generation unit 303 of each calculated delay amount SM_Q. The packet generation unit 303 records the delay amount SM_Q of each Delay_Request message in association with the node information of the slave nodes 400a to 400c that is the transmission source of each Delay_Request message.

  Next, the master node 300 transmits a Delay_Response message storing the delay amount SM_Q and the Delay reception time Tm (1) to each of the slave nodes 400a to 400c (step S404). Specifically, the packet generation unit 303 generates a Delay_Response message storing the delay amount SM_Q and time information Tm (1) corresponding to each of the slave nodes 400a to 400c, and transfers the Delay_Response message to the packet transmission unit 304. Then, the packet transmission unit 304 unicasts each Delay_Response message to the slave nodes 400a to 400c.

  Next, the slave second process by the slave node 400 will be described with reference to FIG. First, the slave node 400 receives a Delay_Response message from the master node 300 (step S501). Specifically, the packet receiving unit 401 receives a Delay_Response message from the master node 300 and transfers the received Delay_Response message to the time synchronization control unit 405.

  Next, the slave node 400 extracts and records the delay amount SM_Q and the delay reception time Tm (1) from the received Delay_Response message (step S502). Specifically, the packet analysis unit 701 of the time synchronization control unit 405 extracts and acquires the delay amount SM_Q and the delay reception time Tm (1) stored in the payload part of the delay_response message in response to the reception of the delay_response message. . Then, the packet analysis unit 701 notifies the offset calculation unit 703 of the acquired delay amount SM_Q and Delay reception time Tm (1).

Next, the slave node 400 calculates values of the time difference MS_Diff and the time difference SM_Diff (step S503). Specifically, the offset calculation unit 703 calculates and holds values of the time difference MS_Diff and the time difference SM_Diff based on the following two expressions (Expression 12 and Expression 13).
MS_Diff = Ts (0)-Tm (0) (12)
SM_Diff = Tm (1)-Ts (1) Equation 13

Next, the slave node 400 calculates Offset (step S504). Specifically, the offset calculation unit 703 calculates Offset based on the time difference MS_Diff, the time difference SM_Diff, the delay amount MS_Q, and the delay amount SM_Q according to the following Expression 14. Then, the offset calculation unit 703 notifies the time adjustment unit 704 of the calculated Offset value.
Offset = {(MS_Diff-SM_Diff)-(MS_Q-SM_Q)} / 2 Equation 14

Equation 14 is obtained as follows. First, the following Expression 15 is obtained from the time difference MS_Diff and the delay amount MS_Q.
MS_Diff = Propagation_Delay + MS_Q + Offset ・ ・ ・ Equation 15
Further, the following Expression 16 is obtained from the time difference SM_Diff and the delay amount SM_Q.
SM_Diff = Propagation_Delay + SM_Q-Offset ・ ・ ・ Equation 16
From the equations 15 and 16, the above equation 14 is obtained. Note that propagation_Delay in Expression 15 and Expression 16 represents the amount of propagation delay between the master node 300 and the slave node 400.

  Returning to the description of the processing shown in FIG. After the process of step S504, the slave node 400 adjusts the slave time using the calculated offset value (step S505). Specifically, the time adjustment unit 704 delays the slave time by Offset when Offset is a positive value, and advances the slave time by Offset when Offset is a negative value. By adjusting the slave time, the slave time is synchronized with the master time of the master node 300.

  14 and 15 are sequence diagrams illustrating a specific example of time synchronization processing by the communication system 1. First, a specific example of time synchronization processing by the communication system 1 will be described with reference to FIG. In FIG. 14, the offset of the slave node 400 with respect to the master node 300 is “3”, the delay amount Propagation_Delay of the propagation delay between the master node 300 and the slave node 400 is “3”, and the queue from the master node 300 to the slave node 400 The delay amount MS_Q of the ing delay is “0”, and the delay amount SM_Q of the queuing delay from the slave node 400 to the master node 300 is “0”. In FIG. 14 and FIG. 15, for convenience of explanation, the master time and the slave time are indicated by integer values instead of the notation of hour / minute / second.

  In the first master process, the Sync transmission time Tm (0) is “4”. In the first slave process, the Sync reception time Ts (0) is “10”, and the Delay transmission time Ts (1) is “15”. In the second master process, the delay reception time Tm (1) is “15”. The delay amount MS_Q of the queuing delay from the master node 300 to the slave node 400 is measured as “0” by the delay measuring unit 403 in the first slave process. Further, the delay amount SM_Q of the queuing delay from the slave node 400 to the master node 300 is measured as “0” by the delay measuring unit 306 in the second master process. In the slave second process, the offset calculation unit 703 of the slave node 400 calculates the value of Offset as “3” based on the above values as follows.

MS_Diff = Ts (0)-Tm (0) = 10-4 = 6
SM_Diff = Tm (1)-Ts (1) = 15-15 = 0
Offset = {(MS_Diff-SM_Diff)-(MS_Q-SM_Q)} / 2 = {(6-0)-(0-0)} / 2 = 3

  FIG. 14 shows a sequence under a condition where Offset is “3”, and Offset can be accurately calculated by the time synchronization processing of the communication system 1 as described above.

  Next, a specific example of time synchronization processing by the communication system 1 will be described with reference to FIG. In FIG. 15, the offset of the slave node 400 with respect to the master node 300 is “4”, the delay amount Propagation_Delay of the propagation delay between the master node 300 and the slave node 400 is “3”, and the queue from the master node 300 to the slave node 400 The delay amount MS_Q of the ing delay is “2”, and the delay amount SM_Q of the queuing delay from the slave node 400 to the master node 300 is “3”.

  In the first master process, the Sync transmission time Tm (0) is “4”. In the first slave process, the Sync reception time Ts (0) is “13”, and the Delay transmission time Ts (1) is “17”. In the second master process, the delay reception time Tm (1) is “19”. The delay amount MS_Q of the queuing delay from the master node 300 to the slave node 400 is measured as “2” by the delay measurement unit 403 in the first slave process. Further, the delay amount SM_Q of the queuing delay from the slave node 400 to the master node 300 is measured as “3” by the delay measuring unit 306 in the second master process. In the slave second process, the offset calculation unit 703 of the slave node 400 calculates the value of Offset as “4” as follows based on the above values.

MS_Diff = Ts (0)-Tm (0) = 13-4 = 9
SM_Diff = Tm (1)-Ts (1) = 19-17 = 2
Offset = {(MS_Diff-SM_Diff)-(MS_Q-SM_Q)} / 2 = {(9-2)-(2-3)} / 2 = 4

  Note that FIG. 15 is a sequence under a condition where Offset is “4”, and even when the queuing delay is not zero, Offset is accurately calculated by the time synchronization processing of the communication system 1 as described above. It is possible to do.

  FIG. 16 is a diagram illustrating a probability distribution of delay amounts measured in the communication system 1. In the experiment in FIG. 16, a network emulator is connected instead of the packet network PN, a delay amount is added to the packet of the Sync message periodically transmitted from the master node 300, and the delay measurement unit 403 of the slave node 400 The amount of delay was measured. FIG. 16 shows the distribution of the delay amount added by the network emulator and the distribution of the delay amount measured by the slave node 400. The horizontal axis of FIG. 16 represents the delay amount, and the vertical axis represents the probability. In both cases of the uniform distribution and the Poisson distribution, the measured delay amount distribution substantially coincides with the delay amount distribution added by the network emulator. Therefore, it is clear that the delay measurement unit 403 can correctly measure the delay amount MS_Q. Since the delay measuring unit 306 of the master node 300 performs the same operation as the delay measuring unit 403 of the slave node 400, it is clear that SM_Q can be correctly measured. Therefore, it is clear that the offset value is accurately calculated by the time synchronization process by the communication system 1, and the slave time can be accurately synchronized with the master time.

  According to the communication system 1 described above, the delay measurement unit 403 of the slave node 400 accurately measures the delay amount MS_Q of the queuing delay from the master node 300 to the slave node 400. Further, the delay measuring unit 306 of the master node 300 accurately measures the delay amount SM_Q of the queuing delay from the slave node 400 to the master node 300. Then, by notifying the slave node 400 of the delay amount SM_Q from the master node 300, the slave node 400 can individually recognize the delay amount of the bidirectional queuing delay between the master node 300 and the slave node 400. . This eliminates the error caused by the actual difference in bidirectional queuing delay compared to the case of calculating Offset assuming that the bidirectional queuing delay is equal as in Pure IEEE1588. It becomes possible to realize time synchronization with higher accuracy.

  Further, in the communication system 1, the delay amount of the queuing delay in each direction can be measured only by the master node 300 and the slave node 400. Therefore, it is not necessary to implement a special function such as the TC function in the relay node in the packet network PN, and it is possible to cope with the existing relay node. In other words, compared to IEEE 1588v2 w / TC, which needs to implement the TC function for the relay node, there is no need to replace the relay node, the cost required for the introduction can be reduced, and the introduction is easy. is there.

<Modification>
The delay measurement unit 306 may be configured using a packet buffer instead of the packet counter 501. When receiving the packet of the Delay_Request message from the packet receiving unit 401, the packet buffer accumulates the received packet in the buffer. Further, the packet buffer outputs accumulated packets according to the frequency determined by the clock generation unit 301. FIG. 17 is a diagram illustrating an outline of processing of the delay measurement unit 306 when configured using a packet buffer. In FIG. 17, the vertical axis represents the accumulation amount in the buffer, and represents a high accumulation amount from bottom to top. The horizontal axis represents time and progresses from left to right. A plurality of broken lines arranged at equal intervals in the vertical direction represent the timing at which a packet of a Delay_Request message is received when no queuing delay occurs. The arrow pointing upward indicates the timing when the packet of the Delay_Request message is actually received. When a packet of a Delay_Request message is received, the amount of accumulation in the packet buffer is increased by the number of received bits. When the vertically extending broken line and the upward arrow coincide with each other on the time axis, that is, when a Delay_Request message packet is received without causing a queuing delay, the read timing (accumulation amount is The time width between the timing (decrease timing) and the newly received timing (timing at which the accumulation amount increases) is the minimum Tmin. On the other hand, when a queuing delay occurs, the above time width becomes a value larger than Tmin. At this time, the difference between the minimum value Tmin and the time width is equivalent to the delay amount of the generated queuing delay.

  Note that any of the configurations of the delay measurement unit 306 described above is merely an example of a configuration for measuring a delay, and other configurations may be employed as long as the configuration can measure the delay amount SM_Q of the queuing delay. . The same applies to the delay measurement unit 403.

[Second Embodiment]
In the first embodiment of the communication system 1, the master node 300 measures the delay amount SM_Q, stores it in the Delay_Response message, and transmits it to the slave node 400. However, in the IEEE1588 standard, although there is a field for storing the Delay reception time Tm (1) in the Delay_Response message, there is no field for storing the delay amount SM_Q. Therefore, in the first embodiment, it is necessary to change the standard format of the Delay_Response message. Therefore, the second embodiment of the communication system 1 makes it possible to realize time synchronization processing without changing the standard format of the Delay_Response message. Hereinafter, the second embodiment of the communication system 1 will be described focusing on differences from the first embodiment.

[Master node]
FIG. 18 is a functional block diagram illustrating a functional configuration of the master node 300 in the second embodiment. The master node 300 in the second embodiment is different from the master node 300 in the first embodiment in that it includes a packet generation unit 303a instead of the packet generation unit 303, and the other configurations are the same.

  The packet generation unit 303a differs from the packet generation unit 303 in the processing related to the Delay_Response message, and the other configuration is the same. The packet generation unit 303a corrects the Delay reception time Tm (1) as the corrected Delay reception time Tm (2) (correction time) using the delay amount SM_Q. Specifically, the packet generation unit 303a calculates the corrected delay reception time Tm (2) as a result of subtracting the delay amount SM_Q from the delay reception time Tm (1). Then, the packet generation unit 303a stores the corrected delay reception time Tm (2) in the Delay_Response message and sends it to the packet transmission unit 304.

[Slave node]
FIG. 19 is a functional block diagram illustrating a functional configuration of the slave node 400 according to the second embodiment. The slave node 400 according to the second embodiment is different from the slave node 400 according to the first embodiment in that the slave node 400 includes a time synchronization control unit 405a instead of the time synchronization control unit 405, and other configurations are the same.

  The time synchronization control unit 405a is different from the time synchronization control unit 405 in that the corrected Delay reception time Tm (2) is used as the reception time information of the Delay_Request message and the delay amount SM_Q is not used.

  FIG. 20 is a functional block diagram illustrating a functional configuration of the time synchronization control unit 405a in the second embodiment. The time synchronization control unit 405a in the second embodiment is different from the time synchronization control unit 405 in the first embodiment in that it includes a packet analysis unit 701a and an offset calculation unit 703a instead of the packet analysis unit 701 and the offset calculation unit 703. Other configurations are the same.

  The packet analysis unit 701a differs from the packet analysis unit 701 in the processing related to the Delay_Response message, and the other configuration is the same. The packet analysis unit 701a extracts the corrected delay reception time Tm (2) from the Delay_Response message, and notifies the offset calculation unit 703a of the extracted corrected delay reception time Tm (2).

  The offset calculation unit 703a differs from the offset calculation unit 703 in that the offset is calculated using the corrected delay reception time Tm (2) instead of the delay reception time Tm (1). Details of the processing of the offset calculation unit 703a will be described later.

[Operation]
Next, the flow of processing of each device of the communication system 1 in the second embodiment will be described. However, since the master first process and the slave first process are the same as the processes in the first embodiment (FIGS. 10 and 11), the description thereof is omitted.

FIG. 21 is a flowchart showing the flow of the master second process in the second embodiment. In FIG. 21, the same processes as those in FIG. In the second embodiment, after step S403, the master node 300 calculates a corrected delay reception time Tm (2) (step S411). Specifically, the packet generation unit 303a calculates the corrected delay reception time Tm (2) by the following equation 17 using the delay amount SM_Q and the delay reception time Tm (1).
Tm (2) = Tm (1)-SM_Q Equation 17

  At this time, the packet generation unit 303a calculates a corrected delay reception time Tm (2) for each of the slave nodes 400a to 400c. Then, the packet generation unit 303a records the corrected delay reception time Tm (2) in association with the node information of the slave nodes 400a to 400c that is the transmission source of the Delay_Request message. The corrected Delay reception time Tm (2) indicates the reception time when the Delay_Request message is transferred without adding a queuing delay.

  Next, the master node 300 transmits a Delay_Response message storing the calculated corrected Delay reception time Tm (2) to the slave node 400 (step S412). Specifically, the packet generation unit 303a generates a Delay_Response message storing the corrected Delay reception time Tm (2) for each of the slave nodes 400a to 400c, and sends it to the packet transmission unit 304. The packet transmission unit 304 unicasts a Delay_Response message to each of the slave nodes 400a to 400c.

  FIG. 22 is a flowchart showing the flow of the slave second process in the second embodiment. In FIG. 22, the same processes as those in FIG. In the second embodiment, after the process of step S501, the slave node 400 extracts and records the corrected delay reception time Tm (2) from the Delay_Response message (step S511). Specifically, the packet analysis unit 701a of the time synchronization control unit 405a extracts and records the corrected Delay reception time Tm (2) stored in the payload part of the Delay_Response message in response to reception of the Delay_Response message. Then, the packet analysis unit 701a notifies the offset calculation unit 703a of the corrected delay reception time Tm (2).

Next, the slave node 400 calculates values of the time difference MS_Diff and the correction time difference SM_Diff2 (step S512). At this time, the process for calculating the time difference MS_Diff is the same as in the first embodiment. The offset calculation unit 703a calculates a corrected time difference SM_Diff2 based on the following Expression 17 using the Delay transmission time Ts (1) and the corrected Delay reception time Tm (2).
SM_Diff2 = Tm (2)-Ts (1) Equation 17

Next, the slave node 400 calculates Offset using the time difference MS_Diff, the correction time difference SM_Diff2, and the delay amount MS_Q (step S513). Specifically, the offset calculation unit 703a calculates Offset by the following Expression 18 based on the time difference MS_Diff, the correction time difference SM_Diff2, and the delay amount MS_Q. The offset calculation unit 703a notifies the time adjustment unit 704 of the calculated Offset value.
Offset = {(MS_Diff-SM_Diff2)-MS_Q} / 2 ... Equation 18

Equation 18 is obtained as follows. First, the following Expression 19 is obtained from the time difference MS_Diff and the delay amount MS_Q. Equation 19 is the same as Equation 15.
MS_Diff = Propagation_Delay + MS_Q + Offset ・ ・ ・ Equation 19
Further, the following equation 20 is obtained from the corrected time difference SM_Diff2.
SM_Diff2 = Propagation_Delay-Offset ・ ・ ・ Equation 20
From the equations 19 and 20, the above equation 18 is obtained. Note that propagation_Delay in Expression 19 and Expression 20 also represents the amount of propagation delay between the master node 300 and the slave node 400, as described above.

  FIG. 23 is a sequence diagram illustrating a specific example of time synchronization processing by the communication system 1 in the second embodiment. In FIG. 23, the offset of the slave node 400 with respect to the master node 300 is “4”, the delay amount Propagation_Delay of the propagation delay between the master node 300 and the slave node 400 is “3”, and the queue from the master node 300 to the slave node 400 The delay amount MS_Q of the ing delay is “2”, and the delay amount SM_Q of the queuing delay from the slave node 400 to the master node 300 is “3”.

In the first master process, the Sync transmission time Tm (0) is “4”. In the first slave process, the Sync reception time Ts (0) is “13”, and the Delay transmission time Ts (1) is “17”. In the second master process, the delay reception time Tm (1) is “19”. The delay amount MS_Q of the queuing delay from the master node 300 to the slave node 400 is measured as “2” by the delay measurement unit 403 in the first slave process. Further, the delay amount SM_Q of the queuing delay from the slave node 400 to the master node 300 is measured as “3” by the delay measuring unit 306 in the second master process. The packet generation unit 303a of the master node 300 calculates the corrected delay reception time Tm (2) as follows.
Tm (2) = Tm (1)-SM_Q = 19-3 = 16

In the second slave process, the offset calculation unit 703a of the slave node 400 calculates the value of Offset as “4” based on the above values as follows.
MS_Diff = Ts (0)-Tm (0) = 13-4 = 9
SM_Diff2 = Tm (2)-Ts (1) = 16-17 = -1
Offset = {(MS_Diff-SM_Diff2)-MS_Q} / 2 = {(9-(-1))-2} / 2 = 4

  Note that FIG. 23 shows a sequence under a condition where Offset is “4”, and even when the Delay_Response message does not include a field for storing the delay amount SM_Q, the communication system 1 as described above. Offset can be accurately calculated by time synchronization processing.

  In the communication system 1 in the second embodiment configured as described above, the time synchronization process is performed with the same accuracy as the communication system 1 in the first embodiment without providing a field for storing the delay amount SM_Q in the Delay_Response message. Can be executed. Accordingly, it is possible to use a standard format Delay Response message. Therefore, for example, there is an effect that it is possible to reduce cost and time when the communication system 1 is mounted.

[Third Embodiment]
In the first embodiment and the second embodiment described above, the master node 300 and the slave node 400 measure the delay amounts MS_Q and SM_Q, so that the bidirectional delay between the master and the slave is maintained without changing the existing relay node. Realized highly accurate time synchronization considering the asymmetry of. On the other hand, in the third embodiment, all relay nodes are replaced by arranging nodes (hereinafter referred to as “emulation nodes”) for measuring the respective delay amounts in the preceding stage of each of the master node 300 and the slave node 400. Without realizing IEEE1588v2 w / TC.

  FIG. 24 is a system configuration diagram of the communication system 1 according to the third embodiment. The communication system 1 in the third embodiment includes a master node 300, slave nodes 400 (400a to 400c), an emulation node 800 (800a to 800d), and a packet network PN. Emulation nodes 800a to 800d are arranged in front of slave nodes 400a to 400c and master node 300, respectively. Note that the emulation node 800 may be implemented as a function of a relay node of the packet network PN, or may be implemented as a device different from the relay node of the packet network PN. When the emulation node 800 is mounted as a device different from the relay node, for example, it is mounted as a single device and is connected to the master node 300 and the slave node 400. Hereinafter, the third embodiment of the communication system 1 will be described focusing on differences from the first embodiment.

[Master node]
FIG. 25 is a functional block diagram showing a functional configuration of the master node 300 in the third embodiment. The master node 300 in the third embodiment operates based on IEEE1588v2 w / TC. Specifically, the master node 300 in the third embodiment is different from the master node 300 in the first embodiment in that it includes a packet generation unit 303b instead of the packet generation unit 303 and does not include a delay measurement unit 306. Other configurations are the same.

  The packet generation unit 303b differs from the packet generation unit 303 in the processing related to the Delay_Response message, and the other configuration is the same. In response to the reception of the Delay_Request message, the packet generation unit 303b acquires the Delay reception time Tm (1) and extracts the CF_SM value from the Delay_Request message. Then, the packet generation unit 303b generates a Delay_Response message that stores the Delay reception time Tm (1) and the CF_SM value.

[Slave node]
FIG. 26 is a functional block diagram illustrating a functional configuration of the slave node 400 according to the third embodiment. The slave node 400 in the third embodiment operates based on IEEE1588v2 w / TC. Specifically, the slave node 400 in the third embodiment differs from the slave node 400 in the first embodiment in that it includes a time synchronization control unit 405b instead of the time synchronization control unit 405 and does not include a delay measurement unit 403. Different, other configurations are the same.

  The time synchronization control unit 405b is different from the time synchronization control unit 405 in that the offset is obtained using the CF value (CF_MS, CF_SM) instead of the delay amount SM_Q and the delay amount MS_Q, and the other configuration is the same.

  FIG. 27 is a functional block diagram illustrating a detailed functional configuration of the time synchronization control unit 405b. The time synchronization control unit 405b is different from the time synchronization control unit 405 in that a packet analysis unit 701b is provided instead of the packet analysis unit 701, and an offset calculation unit 703b is provided instead of the offset calculation unit 703, and other configurations are the same. It is.

  The packet analysis unit 701b is different from the packet analysis unit 701 in processing related to the Sync message and the Delay_Response message. Specifically, when receiving the Sync message, the packet analysis unit 701b refers to the slave clock unit 404, acquires the Sync reception time Ts (0), and extracts the CF value CF_MS from the Sync message. The packet analysis unit 701b notifies the offset calculation unit 703b of the extracted Sync reception time Ts (0) and the CF value CF_MS. Further, when receiving the Delay_Response message, the packet analysis unit 701b extracts the stored Delay reception time Tm (1) and the CF value CF_SM and notifies the offset calculation unit 703b.

  The offset calculation unit 703b transmits and receives Sync message and Delay_Request message transmission / reception time information (Sync transmission time Tm (0), Sync reception time Ts (0), Delay transmission time Ts (1), Delay reception time Tm (1)), CF Calculate Offset using the values CF_MS and CF_SM. Note that the CF values are two values CF_MS and CF_SM stored in the Correction Field of the Delay Response message. CF_MS has the same value as the delay amount MS_Q, and CF_SM has the same value as the delay amount SM_Q. Therefore, the offset calculation unit 703b calculates the value of Offset by replacing the values of MS_Q and SM_Q with CF_MS and CF_SM, respectively, in Equation 14 above.

[Emulation node]
FIG. 28 is a functional block diagram showing a functional configuration of the emulation node 800 in the third embodiment. The emulation node 800 includes a packet reception unit 801, a PLL unit 402, a delay measurement unit 803, a clock unit 804, a TC processing unit 805, and a packet transmission unit 806. The PLL unit 402 has the same configuration as the PLL unit 402 included in the slave node 400 in the first embodiment. The clock unit 804 has the same configuration as the slave clock unit 404 in the first embodiment. The emulation node 800 may include a CPU, a memory, an auxiliary storage device, a communication interface, and the like connected by a bus, for example, and may be configured as a device including the above-described functional units by executing a time synchronization program.

  The configuration of the delay measurement unit 803 is different between the emulation node 800d arranged in the preceding stage of the master node 300b and the emulation nodes 800a to 800c arranged in the preceding stage of the slave node 400b. The delay measurement unit 803 of the emulation node 800d has the same configuration as the delay measurement unit 306 of the master node 300 in the first embodiment. On the other hand, the delay measurement unit 803 of the emulation nodes 800a to 800c has the same configuration as the delay measurement unit 403 of the slave node 400 in the first embodiment. In either case, the delay measurement unit 803 notifies the TC processing unit 805 of the measurement result.

  When receiving the Sync message or the Delay_Request message, the packet receiving unit 801 transfers the received message to the TC processing unit 805 and acquires the reception time of each message with reference to the clock unit 804. Then, the packet reception unit 801 notifies the packet transmission unit 806 of the reception time of each message. Further, when receiving the Follow_up message or the Delay_Response message, the packet receiving unit 801 transfers the packet receiving unit 801 to the packet transmitting unit 806 as it is.

  The delay measuring unit 803 measures a delay amount of a queuing delay until the message reaches the emulation node 800 (hereinafter referred to as “preliminary delay amount”) MS_Q2 and SM_Q2. As described above, the configuration of the delay measurement unit 803 is the same as that of the delay measurement unit 403 of the slave node 400 in the first embodiment, and the delay amount calculated as a result of the same processing as the delay measurement unit 403 is the same. Represents the amount of preliminary delay.

  The TC processing unit 805 records the spare delay amounts MS_Q2 and SM_Q2 as CF values CF_MS and CF_SM in the Correction Field of the Sync message and Delay_Request message received from the packet receiving unit 801, respectively, and transfers them to the packet transmitting unit 806.

  When the packet transmission unit 806 transmits the Sync message or the Delay_Request message from the TC processing unit 805, the packet transmission unit 806 refers to the clock unit 804 and acquires the transmission time. Then, the packet transmission unit 806 calculates the stay time in the node based on the transmission time and the reception time notified from the packet reception unit 801. The staying time in the node represents the time during which the packet stayed in the own device. Then, the packet transmission unit 806 adds the stay time in the node to the CF value stored in the Correction Field, and transfers it to the packet network PN or each destination node (master node 300 or slave node 400). By adding the stay time in the node to the preliminary delay amounts MS_Q2 and SM_Q2 which are CF values, the CF value after the addition becomes the same value as the delay amounts MS_Q and SM_Q. Further, the packet transmission unit 806 transfers the Follow_up message and the Delay_Response message as they are to the packet network PN or each destination node (master node 300 or slave node 400).

[Operation]
Next, the processing flow of each device of the communication system 1 in the third embodiment will be described. However, since the master first process is the same as the process (FIG. 10) in the first embodiment, the description is omitted.

  FIG. 29 is a flowchart showing the flow of the slave first process in the third embodiment. In FIG. 29, the same processes as those in FIG. In the third embodiment, after the process of step S302, the slave node 400 extracts CF_MS from the received Sync message (step S321). Specifically, the packet analysis unit 701b of the time synchronization control unit 405b extracts CF_MS from the received Sync message and notifies the offset calculation unit 703b of CF_MS. Then, after the process of step S311, the slave node 400 executes the processes of S303 to S306.

  FIG. 30 is a flowchart showing the flow of the master second process in the third embodiment. In FIG. 30, the same processes as those in FIG. In the third embodiment, after step S402, the master node 300 extracts CF_SM from the received Delay_Request message (step S421). Specifically, the packet generation unit 303b extracts CF_SM from the received Delay_Request message, and holds it together with the node information of each slave node 400 that is the transmission source of the Delay_Request message.

  Next, the master node 300 transmits a Delay_Response message storing the CF value CF_SM and the Delay reception time Tm (1) to each of the slave nodes 400a to 400c (step S422). Specifically, the packet generation unit 303b generates a Delay_Response message storing the CF value CF_SM and time information Tm (1) corresponding to each of the slave nodes 400a to 400c, and transfers the Delay_Response message to the packet transmission unit 304. Then, the packet transmission unit 304 unicasts each Delay_Response message to the slave nodes 400a to 400c.

  FIG. 31 is a flowchart showing the flow of the slave second process in the third embodiment. In FIG. 31, the same processes as those of FIG. In the third embodiment, after step S501, the slave node 400 extracts and records the CF value CF_SM and the delay reception time Tm (1) from the received Delay_Response message (step S521). Specifically, the packet analysis unit 701b of the time synchronization control unit 405b extracts and acquires the CF value CF_SM and the Delay reception time Tm (1) stored in the payload part of the Delay_Response message in response to the reception of the Delay_Response message. . Then, the packet analysis unit 701b notifies the offset calculation unit 703b of the acquired CF value CF_SM and Delay reception time Tm (1).

Next, the slave node 400 calculates values of the time difference MS_Diff and the time difference SM_Diff (step S522). Specifically, the offset calculation unit 703b calculates and holds values of the time difference MS_Diff and the time difference SM_Diff based on the following two expressions (Expression 21 and Expression 22).
MS_Diff = (Ts (0)-CF_MS)-Tm (0) ... Equation 21
SM_Diff = (Tm (1)-CF_SM)-Ts (1) Equation 22

  Next, the slave node 400 calculates Offset (step S523). Specifically, the offset calculation unit 703b calculates Offset by the following Expression 23 based on the time difference MS_Diff and the time difference SM_Diff. Then, the offset calculation unit 703b notifies the time adjustment unit 704 of the calculated Offset value.

Offset = (MS_Diff-SM_Diff) / 2
= {(Ts (0)-CF_MS)-Tm (0)-((Tm (1)-CF_SM)-Ts (1))} / 2
= {Ts (0)-CF_MS-Tm (0)-Tm (1) + CF_SM + Ts (1)} / 2 Equation 23

Equation 23 is obtained as follows. First, the time difference MS_Diff is expressed by the following equation 24.
MS_Diff = Propagation_Delay + Offset ・ ・ ・ Equation 24
Further, the time difference SM_Diff is expressed by the following Expression 25.
SM_Diff = Propagation_Delay-Offset ・ ・ ・ Equation 25
Then, the above equation 23 is obtained from the equations 24 and 25. Propagation_Delay in Expression 24 and Expression 25 represents the amount of propagation delay between the master node 300 and the slave node 400.

  Note that the offset calculation unit 703b may be configured to calculate Offset using Expressions 12 to 14 as in the first embodiment by replacing CF_SM and CF_MS with SM_Q and MS_Q, respectively.

  FIG. 32 is a flowchart showing the flow of processing by the emulation node 800 in the third embodiment. First, the emulation node 800 receives a 1588 message (step S601). Specifically, the packet receiving unit 801 receives 1588 packets. If the received 1588 message is a Sync message or a Delay_Request message, the emulation node 800 measures the preliminary delay amount of the queuing delay (step S602). Specifically, the delay calculation unit 604 of the delay measurement unit 803 calculates the spare delay amounts MS_Q2 and SM_Q2.

  Next, the emulation node 800 records the preliminary delay amounts MS_Q2 and SM_Q2 as CF values (step S603). Specifically, the TC processing unit 805 records the preliminary delay amounts MS_Q2 and SM_Q2 as CF values CF_MS and CF_SM in the Correction field of the Sync message or Delay_Request message, respectively. Next, the emulation node 800 measures the stay time in the node (step S604). Specifically, the packet transmission unit 806 calculates the stay time in the node based on the reception time and transmission time of the Sync message or Delay_Request message. Next, the emulation node 800 adds the stay time in the node to the CF value (step S605). Specifically, the packet transmission unit 806 adds the stay time in the node to the CF value stored in the Correction Field. Then, the emulation node 800 transmits a 1588 message (step S606). Specifically, the packet transmission unit 806 transfers the Sync message or Delay_Request message after the in-node residence time is added to the packet network PN or each node (master node 300 or slave node 400) serving as the destination.

  On the other hand, when the 1588 message received in step S601 is a message other than the Sync message and the Delay_Request message, the emulation node 800 transmits the 1588 message (step S607). Specifically, the packet transmission unit 806 transfers the received message to the packet network PN or each node (master node 300 or slave node 400) serving as a destination.

  FIG. 33 is a sequence diagram illustrating a specific example of time synchronization processing by the communication system 1 according to the third embodiment. In FIG. 33, the offset of the slave node 400a with respect to the master node 300 is “4”, the delay amount Propagation_Delay of the propagation delay between the master node 300 and the slave node 400a is “3”, and the queue from the master node 300 to the slave node 400a. The delay amount MS_Q of the ing delay is “2”, and the delay amount SM_Q of the queuing delay from the slave node 400a to the master node 300 is “3”.

  In the first master process, the Sync transmission time Tm (0) is “4”. In the first slave process, the Sync reception time Ts (0) is “13”, and the Delay transmission time Ts (1) is “17”. In the second master process, the delay reception time Tm (1) is “19”.

  The emulation node 800a measures the queuing delay (preliminary delay amount) MS_Q2 added between the master node 300 and the emulation node 800a with respect to the Sync message. Also, the emulation node 800a adds the in-node residence time Ts_sync in its own device to the spare delay amount MS_Q2, and stores it in the Sync message as CF_MS = 2. Then, the emulation node 800a transfers the Sync message to the slave node 400a.

  The emulation node 800d measures the queuing delay (preliminary delay amount) SM_Q2 added between the slave node 400a and the emulation node 800d in response to the Delay_Request message. Also, the emulation node 800d adds the in-node residence time Ts_dreq in its own device to the spare delay amount SM_Q2, and stores it in the Delay_Request message as CF_SM = 3. Then, the emulation node 800d transfers the Delay_Request message to the master node 300.

In the slave second process, the offset calculation unit 703b of the slave node 400a calculates the value of Offset as “4” as follows based on the above values.
MS_Diff = (Ts (0)-CF_MS)-Tm (0) = (13-2)-4 = 7
SM_Diff = (Tm (1)-CF_SM)-Ts (1) = (19-3)-17 = -1
Offset = (MS_Diff-SM_Diff) / 2 = (7-(-1)) / 2 = 4

  FIG. 33 is a sequence under a condition where Offset is “4”. By the time synchronization control method of the third embodiment, the emulation node 800 substitutes the TC function of the relay node, and is offset by IEEE1588v2 w / TC. As described above, Offset can be accurately calculated by the time synchronization processing of the communication system 1 as described above.

  In the communication system 1 according to the third embodiment configured as described above, the emulation node 800 arranged in the preceding stage of the master node 300 and the slave node 400 is the total value of the queuing delay from the other node to the own device. Measure the preliminary delay amount and store it in the Correction Field of the 1588 message. For this reason, the emulation node 800 accurately measures the delay amount to be stored in the Correction Field without mounting the TC function on the relay node. Therefore, when IEEE 1588v2 w / TC is implemented, it is not necessary to implement the TC function for all relay nodes in the packet network PN. Therefore, there is an effect that it is possible to reduce costs and time when implementing time synchronization control by IEEE1588v2 w / TC.

  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.

300 ... Master node, 301 ... Clock generation unit, 302 ... Master clock unit, 303 ... Packet generation unit (notification unit), 304 ... Packet transmission unit (transmission unit, notification unit), 305 ... Packet reception unit, 306 ... Delay measurement Unit (first delay measurement unit), 400 ... slave node, 401 ... packet reception unit, 402 ... PLL unit, 403 ... delay measurement unit (second delay measurement unit), 404 ... slave clock unit, 405 ... time synchronization control unit , 406 ... Packet transmitter (transmitter), 407 ... Phase comparator, 408 ... LPF, 409 ... PI controller, 410 ... VCO, 411 ... Counter, 501 ... Packet counter, 502 ... Counter maximum value monitor, 503 ... Arrival time counter value monitoring unit, 504... Delay calculation unit, 601... Packet counter, 602 Counter maximum value monitoring unit, 603... Arrival counter value monitoring unit, 604. Delay calculating unit, 701. Packet analyzing unit, 702. Packet generating unit, 703. Offset calculating unit, 704 ... Time adjusting unit, 800 ... Emulation node ( Relay device), 801 ... packet receiving unit, 803 ... delay measuring unit, 804 ... clock unit, 805 ... TC processing unit, 806 ... packet transmitting unit

Claims (10)

A time synchronization system comprising a master node and a slave node that communicate with each other, and a relay device that relays communication between the master node and the slave node, and synchronizes the time at the slave node with the time at the master node,
The master node is
A transmission unit for transmitting a control message to the slave node;
A receiver for receiving a control message from the slave node;
With
The master node or the relay device is
A first delay measuring unit that measures a first delay amount representing a queuing delay received in a communication path by a control message transmitted from the slave node to the master node;
A notification unit for notifying the slave node of the first delay amount measured by the first delay measurement unit;
With
The slave node or the relay device is
A second delay measuring unit that measures a second delay amount representing a queuing delay received in a communication path by a control message transmitted from the master node to the slave node;
With
The slave node is
A transmitter for transmitting a control message to the master node;
A receiving unit for receiving the control message from the master node;
The difference between the time at the slave node and the time at the master node is calculated using the first delay amount notified from the master node and the second delay amount measured by the second delay measurement unit. A time synchronization control unit that synchronizes the time at the slave node with the time at the master node;
A time synchronization system comprising:   The first delay measurement unit or the second delay measurement unit, based on the amount of packets of the control message received in its own device and the amount of packets that are periodically read, The time synchronization system according to claim 1, wherein the second delay amount is measured.   The first delay measurement unit or the second delay measurement unit includes a buffer for accumulating the control message received in its own device, the timing at which the control message is accumulated in the buffer, and the control message from the buffer. 2. The time synchronization system according to claim 1, wherein the first delay amount or the second delay amount is measured based on a timing at which is read periodically.   The notification unit of the master node calculates a correction time that represents a result of subtracting the first delay amount from a reception time that represents a time when the control message is received at the master node, and is provided in advance in the control message. The time synchronization system according to any one of claims 1 to 3, wherein notification is performed by storing the correction time in a field for storing the reception time. A transmission unit that communicates with a master node and transmits a control message to the master node; a reception unit that receives a control message from the master node; and a queue that the control message transmitted from the master node receives on a communication path A second delay measuring unit that measures a second delay amount representing an in-gear delay, the first delay amount notified from the master node, and the second delay amount measured by the second delay measuring unit. A time synchronization control unit that synchronizes the time with the time in the master node, and a master node provided in a time synchronization system including a slave node,
A transmission unit for transmitting a control message to the slave node;
A receiver for receiving a control message from the slave node;
A first delay measuring unit that measures a first delay amount representing a queuing delay received in a communication path by a control message transmitted from the slave node to the master node;
A notification unit for notifying the slave node of the first delay amount measured by the first delay measurement unit;
A master node comprising: A transmitting unit that communicates with a slave node and transmits a control message to the slave node; a receiving unit that receives a control message from the slave node; and a queuing received by the control message transmitted from the slave node on a communication path Provided in a time synchronization system having a master node comprising: a first delay measurement unit that measures a first delay amount that represents a delay; and a notification unit that notifies the first delay amount measured by the first delay measurement unit. A slave node,
A transmitter for transmitting a control message to the master node;
A receiving unit for receiving the control message from the master node;
A second delay measuring unit that measures a second delay amount representing a queuing delay received in a communication path by a control message transmitted from the master node to the slave node;
Using the first delay amount notified from the master node and the second delay amount measured by the second delay measurement unit of the own device, the time at the slave node and the time at the master node A time synchronization controller that calculates the difference and synchronizes the time at the slave node with the time at the master node;
A slave node comprising: A relay device that relays communication between a master node and a slave node that synchronizes time with the time of the master node,
A first delay measuring unit that measures a first delay amount representing a queuing delay received in a communication path by a control message transmitted from the slave node to the master node;
A control message transmitted from the master node to the slave node measures a second delay amount indicating a queuing delay received in a communication path, and uses the first delay amount and the measured second delay amount. The difference between the time at the slave node and the time at the master node is calculated and measured by the first delay measurement unit for the slave node that synchronizes the time at the slave node with the time at the master node. A notification unit for notifying the first delay amount;
A relay device comprising: A relay device that relays communication between a master node and a slave node that synchronizes time with the time of the master node,
A second delay measuring unit that measures a second delay amount representing a queuing delay received in a communication path by a control message transmitted from the master node to the slave node;
Using the first delay amount indicating the queuing delay received in the communication path from the slave node to the master node and the second delay amount, the time at the slave node and the master node A notifying unit that calculates a difference with time and notifies the second delay amount measured by the second delay measuring unit to the slave node that synchronizes the time at the slave node with the time at the master node;
A relay device comprising: A time synchronization method performed by a time synchronization system that includes a master node and a slave node that communicate with each other, and a relay device that relays communication between the master node and the slave node, and synchronizes the time at the slave node with the time at the master node. And
A transmission step in which the master node transmits a control message to the slave node;
A receiving step in which the master node receives a control message from the slave node;
A first delay measuring step in which the master node or the relay device measures a first delay amount representing a queuing delay received in a communication path by a control message transmitted from the slave node to the master node;
A notification step in which the master node or the relay device notifies the slave node of the first delay amount measured in the first delay measurement step;
A transmission step in which the slave node transmits a control message to the master node;
A receiving step in which the slave node receives the control message from the master node;
A second delay measurement step in which the slave node or the relay device measures a second delay amount representing a queuing delay received in a communication path by a control message transmitted from the master node to the slave node;
The slave node uses the first delay amount notified from the master node and the second delay amount measured in the second delay measurement step, and uses the time at the slave node and the time at the master node. And a time synchronization control step for synchronizing the time at the slave node with the time at the master node;
A time synchronization method comprising: Corresponding to the master node as a time synchronization system that includes a master node and a slave node that communicate with each other and a relay device that relays communication between the master node and the slave node, and synchronizes the time at the slave node with the time at the master node A time synchronization program for operating a first computer, a second computer corresponding to the slave node, and a third computer corresponding to the relay device,
For the first computer,
A transmission step of transmitting a control message to the slave node;
Receiving a control message from the slave node;
And execute
For the first computer or the third computer,
A first delay measurement step of measuring a first delay amount representing a queuing delay received in a communication path by a control message transmitted from the slave node to the master node;
A notification step of notifying the slave node of the first delay amount measured by the first delay measurement step;
And execute
For the second computer or the third computer,
A second delay measurement step of measuring a second delay amount representing a queuing delay received in a communication path by a control message transmitted from the master node to the slave node;
And execute
For the second computer,
A transmission step of transmitting a control message to the master node;
Receiving the control message from the master node;
The difference between the time at the slave node and the time at the master node is calculated using the first delay amount notified from the master node and the second delay amount measured at the second delay measurement step. A time synchronization control step for synchronizing the time at the slave node with the time at the master node;
The program for time synchronization characterized by performing this.

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