KR102064575B1 - Method, apparatus, system and computer program for enhancing the accuracy of Time Synchronization between devices - Google Patents

Abstract

The present invention relates to a method, an apparatus, a system, and a computer program for improving the accuracy of time synchronization between devices. A method, apparatus, system, and computer program capable of improving time synchronization accuracy between devices by estimating the traffic in the communication network in consideration of the period change due to transmission delay, and synchronizing the time between the devices by reflecting the traffic. It is about.
In the present invention, in synchronizing the time between the devices connected to the communication network, the traffic in the communication network is estimated in consideration of the change in the period according to the transmission delay of the time synchronization packet periodically transmitted for time synchronization, and reflects the traffic By synchronizing the time between the devices, even if the traffic in the communication network increases, it is possible to suppress the occurrence of the time synchronization error between the devices accordingly, thereby increasing the time synchronization accuracy between the devices.

Description

Method, apparatus, system and computer program for enhancing the accuracy of Time Synchronization between devices}

The present invention relates to a method, an apparatus, a system and a computer program for improving the accuracy of time synchronization between devices. More particularly, the present invention relates to a method of synchronizing time synchronization packets periodically transmitted for time synchronization in synchronizing time between devices connected to a communication network. A method, apparatus, system, and computer program capable of improving time synchronization accuracy between devices by estimating the traffic in the communication network in consideration of the period change due to transmission delay, and synchronizing the time between the devices by reflecting the traffic. It is about.

A protocol for sharing a reference time is required between network devices in a network.In addition, IRIG-B, Pulse Per Second (PPS), which uses a dedicated line for visual synchronization other than the network line, and a network line are shared to transmit necessary information for a packet. NTP (Network Time Protocol), PTP (Precise Time Protocol) and the like. Among these, the PTP method is defined in the international standards (IEEE 1588 and IEC 61588) as a method for precise time synchronization of microsecond or less. The PTP method periodically exchanges packets including time synchronization information between the time synchronization master device and the slave device to synchronize the time of the slave device with the master device, and simultaneously synchronizes multiple slave devices with one master device. Therefore, PTP is used in many places such as factory automation, automobile control, robot control, smart grid distributed power supply, and power failure diagnosis.

By the way, the time synchronization method using a communication network, such as the PTP method may be very accurate in an ideal environment, but the communication state is not good, such as delayed communication due to the large traffic (traffic), or the time between the time synchronization master and slave If there is a device such as a switch that does not support synchronization, there is a problem that the performance of time synchronization is poor. In this case, if the switch includes a time synchronization function such as a TC (transparent clock), the error may be remarkably reduced, but even in this case, when the traffic of the network is not constant, it is concentrated during time synchronization packet exchange. There remains a problem that the visual synchronization error can be large.

Korean Unexamined Patent Publication No. 10-2009-0032306 (published April 1, 2000)

A method, apparatus, system, and computer program for improving time synchronization accuracy according to an embodiment of the present invention is to synchronize time between devices connected to a communication network, even if traffic in the communication network increases, so that time synchronization between the devices accordingly. It aims at making it possible to suppress the occurrence of an error.

According to an aspect of the present invention, there is provided a method for synchronizing time between devices connected to a communication network, wherein a slave device receives a first time synchronization packet in a first period from a master device. First packet transmission step; A second packet transmission step of receiving, by the slave device, a second time synchronization packet in a second period transmitted after a predetermined time period has elapsed from the master device; A first period calculating step of calculating a time period for the first period by using a reception time of the first time synchronization packet and a reception time of the second time synchronization packet; And a time synchronization step of synchronizing the time of the slave device using the first time synchronization packet in consideration of the time period calculated for the first period.

In this case, the time synchronization step may include estimating a communication network state in the first period in consideration of the time period calculated for the first period; And synchronizing the time of the slave device by using the first time synchronization packet in consideration of the communication network state in the first period.

Here, in the time synchronization step, when the communication network state does not reach a predetermined reference value, the first time synchronization packet is not used for time synchronization for the slave device, or the communication is performed on the first time synchronization packet. Weights according to network conditions may be used for time synchronization with the slave device.

In addition, the time synchronization method according to the present invention includes a third packet transmission step in which the slave device receives a third time synchronization packet in a third period transmitted after a predetermined time period has elapsed from the master device; A second period calculating step of calculating a time period for the second period by using a reception time of the second time synchronization packet and a reception time of the third time synchronization packet; And estimating a communication network state in the first period by comparing the time period calculated for the first period and the time period calculated for the second period.

A program stored in a computer readable medium according to another aspect of the present invention is a program for executing each step of the time synchronization method in a computer.

According to another aspect of the present invention, a slave device device includes: a slave device device for synchronizing time between devices connected to a communication network, the slave device device comprising: a first packet receiving unit receiving a first time synchronization packet in a first period from a master device; A second packet receiver configured to receive a second time synchronization packet in a second period transmitted after a predetermined time period has elapsed from the master device; A first period calculator configured to calculate a time period for the first period by using a reception time of the first time synchronization packet and a reception time of the second time synchronization packet; And a time synchronization unit for synchronizing the time of the slave device using the first time synchronization packet in consideration of the time period calculated for the first period.

In this case, the time synchronization unit may include a communication network state estimating unit estimating a communication network state in the first period in consideration of the time period calculated for the first period; And a time synchronizer configured to synchronize the time of the slave device using the first time sync packet in consideration of the communication network state in the first period.

Here, in the time synchronization unit, when the communication network state does not reach a predetermined reference value, the first time synchronization packet is not used for time synchronization for the slave device, or the communication is performed in the first time synchronization packet. Weights according to network conditions may be used for time synchronization with the slave device.

In addition, the slave device apparatus according to the present invention, a third packet receiving unit for receiving a third time synchronization packet in a third period transmitted after a predetermined time period from the master device; A second period calculator configured to calculate a time period for the second period by using a reception time of the second time synchronization packet and a reception time of the third time synchronization packet; And a communication network state estimator for estimating a communication network state in the first period by comparing the time period calculated for the first period and the time period calculated for the second period.

A time synchronization system according to another aspect of the present invention is a time synchronization system for synchronizing time between devices connected to a communication network, and after transmitting a first time synchronization packet in a first period, after a predetermined time period has elapsed. A master device for transmitting a second time synchronization packet in a second period; And receiving a first time synchronization packet from the master device in a first period and receiving a second time synchronization packet in a second period, and then receiving a reception time of the first time synchronization packet and receiving the second time synchronization packet. A slave device that calculates a time period for the first period by using a time, and synchronizes the time for the master device using the first time synchronization packet in consideration of the time period calculated for the first period. Characterized in that it comprises a.

Method, apparatus, system and computer program for improving the time synchronization precision according to an embodiment of the present invention, in synchronizing the time between the devices connected to the communication network in the transmission delay of the time synchronization packet periodically sent for time synchronization By estimating the traffic in the communication network in consideration of the change in the period, and synchronizing the time between the devices by reflecting this, it is possible to suppress the occurrence of time synchronization error between the devices accordingly even if the traffic in the communication network increases. As a result, the time synchronization accuracy between the devices can be improved.

In addition, since the method, apparatus, system, and computer program for improving the time synchronization accuracy according to an embodiment of the present invention can be implemented without adding an additional device, no additional cost is required, and additional network traffic is also required. It is possible to increase the accuracy of time synchronization between devices without generating.

FIG. 1 is an exemplary diagram illustrating a procedure for exchanging time synchronization communication packets in accordance with the precision time synchronization (PTP, IEEE1588) method.
2 is a block diagram of a time synchronization system according to an embodiment of the present invention.
3 is an exemplary diagram illustrating a time synchronization packet exchange and a time synchronization packet period calculation using the time synchronization packet in the time synchronization method according to an embodiment of the present invention.
4 is a graph for explaining a method of improving the accuracy of time synchronization using the time synchronization packet period calculated according to one embodiment of the present invention.
5 is a flowchart of a time synchronization method according to an embodiment of the present invention.
6 is a block diagram of a time synchronization device according to an embodiment of the present invention.

Technical terms used in the present invention are merely used to describe particular embodiments, it should be noted that it is not intended to limit the present invention. In addition, the technical terms used in the present invention should be interpreted as meanings generally understood by those skilled in the art unless the present invention is defined in any other meaning in the present invention, and is excessively comprehensive. It shall not be construed in the sense of or in the sense of being excessively reduced. In addition, when the technical terminology used in the present invention is an incorrect technical term that does not accurately express the spirit of the present invention, it should be understood as being replaced by a technical term that can be properly understood by those skilled in the art. In addition, the general terms used in the present invention should be interpreted as defined in the dictionary or according to the context before and after, and should not be interpreted in an excessively reduced sense.

Hereinafter, exemplary embodiments of the present invention will be described in detail with reference to the accompanying drawings, and the same or similar components will be given the same reference numerals regardless of the reference numerals and redundant description thereof will be omitted.

In addition, in describing the present invention, when it is determined that the detailed description of the related known technology may obscure the gist of the present invention, the detailed description thereof will be omitted. In addition, it is to be noted that the accompanying drawings are only for easily understanding the spirit of the present invention and should not be construed as limiting the spirit of the present invention by the accompanying drawings.

DETAILED DESCRIPTION Hereinafter, exemplary embodiments of a method and apparatus for improving time synchronization precision according to the present invention will be described in detail with reference to the accompanying drawings.

First, prior to a detailed description of the present invention, a method for synchronizing time between devices using a communication network will be briefly described, and then a detailed configuration of the present invention will be described.

First, FIG. 1 illustrates an example of a method of synchronizing time between devices using a communication network, and illustrates a processing procedure of a time synchronization communication packet for time synchronization in a precision time synchronization (PTP) scheme.

As can be seen in Figure 1, the time synchronization communication packet exchange sequence according to the precision time synchronization (PTP, IEEE1588) scheme is composed of a total of four steps of ①Sync, ②Follow_up, ③Delay_Req, ④ Delay_Resp.

The slave device synchronizes with the time of the master device through the four-stage packet exchange as described above, and each of the master device and the slave device includes a precise timer (usually several ns to several tens of ns units in the PTP method).

First, the time synchronization master device transmits a Sync packet to a slave device through a communication network. At this time, the master device measures the time t ₁ of transmitting the Sync packet with an internal precision timer, and then transmits the Follow_Up packet with time information t ₁ of transmitting the Sync packet. The slave device measures the time of receiving the Sync packet with an internal precision timer (t ₂ ). Subsequently, the slave device can know the start time t ₁ of the sync by receiving the Follow_up packet. Next, the slave device transmits a Delay_Req packet to the master device and simultaneously records a Delay_Req packet transmission time t ₃ . When the Delay_Req packet arrives at the master device, it measures the reception time (t ₄ ) of the Delay_Req packet using an internal timer and transmits the information (t ₄ ) in the Delay_Resp packet to the slave device again. Through this four-stage packet exchange, the slave device can know all of t ₁ , t ₂ , t ₃ , and t _4. Therefore, the time difference (offset _MS) of the slave device with respect to the master device using Equation 1 ), So that the slave device can synchronize its time by calibrating its timer.

However, in the case of correcting the time difference between the master device and the slave device as described above, in the ideal network environment, precise time synchronization of several microseconds or less may be realized. However, when the network situation is not good, for example, time synchronization. When the network traffic at the time of packet exchange is excessive and the transmission of the time synchronization packet is delayed, the error of the time difference calculated by Equation 1 becomes large, so that the accuracy of time synchronization is increased. Lowering problems may occur.

At this time, if the traffic state in the communication network is known, the time synchronization packet exchange may not be performed at that time, or the packet may not be used for time synchronization. However, since the packet exchange for time synchronization is repeatedly performed within a few seconds, very fast real-time updates are required for traffic monitoring, thereby increasing network traffic.

In order to solve the above problems, the present invention estimates the network environment during time synchronization packet exchange, and if it is determined that the network environment at that time is not good, the result of Equation 1 is not applied to the time correction of the slave device. , Or a method of correcting the time at the slave device by using the weight according to the network environment may be used.

More specifically, FIG. 2 illustrates a configuration diagram of the time synchronization system 100 according to an embodiment of the present invention. As shown in FIG. 2, the time synchronization system 100 according to an exemplary embodiment of the present invention may include a master device 110 and a plurality of slave devices 120, 120a, and 120n. The device 110 and the slave device 120 may be connected via the communication network 130.

First, the master device 110 transmits a time synchronization packet to the slave device 120 at a predetermined time period. Subsequently, the master device 110 and the slave device 120 may exchange a series of packets with each other as described above. Accordingly, the slave device 120 may calculate a time difference with respect to the master device 110. Accordingly, the slave device 120 may correct the time difference by synchronizing with the master device 110 by reflecting the calculated time offset.

However, the time synchronization packet transmitted between the master device 110 and the slave device 120 may cause a deviation in transmission time, such as delay in transmission, depending on a traffic state or the like in the communication network 130. In this case, the slave device 120 cannot calculate an accurate time offset with respect to the master device 110, and furthermore, cannot correct the time difference with respect to the master device 110 accurately. do.

On the other hand, in the present invention, the period for the time synchronization packet periodically sent from the master device 110 is measured in the slave device 120 to estimate the traffic in the communication network 130, and reflects the slave device By synchronizing the time at 120, it is possible to improve the time synchronization accuracy at the slave device 120 with respect to the master device 110.

As an embodiment of the present invention, FIG. 3 is a diagram illustrating a time synchronization packet exchange for time synchronization in a precise time synchronization (PTP) scheme and a calculation of a time synchronization packet cycle using the same. Although FIG. 3 illustrates an embodiment in the PTP scheme, the present invention is not necessarily limited thereto. In addition, the present invention is not limited thereto. This can be applied.

In the precise time synchronization (PTP) scheme, as shown in FIG. 3, the master device 110 and the slave device 120 may periodically exchange time synchronization packets, for example, for precise time synchronization. As shown in FIG. 3, four packets can be exchanged in the kth period, such as Sync (k), Follow_up (k), Delay_Req (k), and Delay_Res (k).

At this time, the master device 110 transmits a Sync (k) packet while precisely maintaining the interval (T _k = t _{k + 1,1} -t _{k, 1} ) of each period using a built-in precision timer. In addition, the slave device 120 calculates the interval of each period using a built-in precision timer (T '= t _{k + 1,2} -t _{k, 2} ) and the communication network at the time of transmission of the Sync (k) packet ( The transmission environment such as traffic at 130 is estimated.

Accordingly, the difference (ΔT ' _k = T' _{k -} T ' _k-1 ) of the period calculated by the slave device 120 may be represented as shown in FIG. 4, and if the value ΔT' _k is larger than a predetermined reference value, If large, the slave device 120 does not use the corresponding packet {Sync (k), Follow_up (k), Delay_Req (k), Delay_Res (k)} for the time correction for the master device 110 and then uses the next packet. I can wait.

In the present invention, it is possible to estimate the network environment at the time of time synchronization packet exchange without the need for additional traffic monitoring as described above. In the present invention, assuming that the period of the time synchronization packet is T (generally within a few seconds), the master device 110 generates the packet by precisely controlling this period using a time synchronization precision timer. Subsequently, the slave device 120 estimates the network environment at the time of generating the time synchronization packet by observing the period T by using the time synchronization precision timer when the time synchronization packet is received. On the other hand, the conventional precision time synchronization (PTP) scheme does not use the period T information for time synchronization, and thus does not strictly control the period T and does not restore the period T information upon reception.

Further, the difference ΔT ′ _k of the period calculated by the slave device 120 may be used simply by excluding a packet of the corresponding period k during time correction, but may be used in various ways. For example, may be used in ΔT 'by using the _k if compensation precision timer incorporated in the slave device 120, the ΔT' calculates a predetermined statistic, such as the variance of _k. Or, in the following correction precision timer which is incorporated in the slave device 120, by using a recursive filter (recursive filter), such as a Kalman filter may use the information in the ΔT _'k to the k-th weight of the recursive filter. In addition, as an embodiment of the present invention, the period ΔT ′ _k calculated by the slave device 120 may be variously implemented using various methods of synchronizing by correcting the time with respect to the master device 110.

5 illustrates a flowchart of a time synchronization method according to an embodiment of the present invention. As shown in FIG. 5, a time synchronization method according to an embodiment of the present invention is a method of synchronizing time between devices connected to a communication network, wherein a slave device 1200 receives a first period from a master device 110. A first packet transmission step (S1100) of receiving a first time synchronization packet at, a second in a second period in which the slave device 120 is transmitted after a predetermined time period has elapsed from the master device 110 A second packet transmission step (S1200) of receiving a time synchronization packet, a first period of calculating a time period for the first period by using a reception time of the first time synchronization packet and a reception time of the second time synchronization packet. In consideration of the period calculating step (S1300) and the time period calculated for the first period, the time of the slave device 120 using the first time synchronization packet is determined. A may include a time synchronization step (S1400) for synchronization.

Hereinafter, each step of the time synchronization method according to an embodiment of the present invention will be described in detail with reference to FIGS. 3 and 5.

First, in operation S1100, the slave device 1200 receives a first time synchronization packet in a first period from the master device 110. Referring to FIG. 3, the master device 110 transmits a Sync (k) packet to the slave device 120 through the communication network 130 at a predetermined time t _{k, 1} . At this time, the slave device 120 records the time (t _{k, 2} ) when receiving the Sync (k) packet. Subsequently, the slave device 120 may further exchange a series of packets to calculate a time offset with the master device 110 (Follow_up (k), Delay_Req (k), Delay_Resp (k) packets. Etc).

Subsequently, in operation S1200, the slave device 120 receives a second time synchronization packet in a second period transmitted after a predetermined time period elapses from the master device 110. Referring to FIG. 3, the master device 110 transmits a Sync (k + 1) packet to the slave device 120 through the communication network 130 after a predetermined time period T _k elapses. At this time, the slave device 120 also records a time point (t _{k + 1,2} ) when the Sync (k + 1) packet is received. In addition, the slave device 120 may further exchange a series of packets to calculate a time offset with the master device 110 (Follow_up (k + 1), Delay_Req (k + 1), Delay_Resp). (k + 1) packets, etc.).

Next, in step S1300, the time period for the first period is calculated using the reception time of the first time synchronization packet and the reception time of the second time synchronization packet. In the case of FIG. 3, the reception time t _{k, 2 of} the first time synchronization packet Sync (k) and the reception time t _{k + of} the second time synchronization packet Sync (k + 1) measured above. _1,2 ) to _calculate the time period T ' _k = t _{k + 1,2} -t _{k, 2} for the first period.

Finally, in step S1400, the time of the slave device 120 is synchronized using the first time synchronization packet in consideration of the time period calculated for the first period.

Further, the step S1400 may include estimating a communication state such as traffic of the communication network 130 in the first period in consideration of the time period calculated for the first period, and the communication network 130 in the first period. Taking into consideration the state), the method may include synchronizing the time of the slave device 120 using the first time synchronization packet.

More specifically, in step S1400, when the communication network 130 state does not reach a predetermined reference value, the first time synchronization packet is not used for time synchronization with respect to the slave device 120, or the first time synchronization packet 130 is not used. A time synchronization packet may be weighted according to the state of the communication network 130 to be used for time synchronization of the slave device 120.

Furthermore, in the time synchronization method according to an embodiment of the present invention, the slave device 120 receives a third time synchronization packet in a third period transmitted after a predetermined time period passes from the master device 110. A second period calculating step of calculating a time period for the second period by using a third packet transmission step of receiving, a reception time of the second time synchronization packet, and a reception time of the third time synchronization packet; The method may further include estimating the state of the communication network 130 in the first period by comparing the time period calculated for the period and the time period calculated for the second period.

That is, the time period in the first period k is calculated using the time synchronization packet in the first period k, and further, this is the time synchronization in the second period (ie, another period such as k + 1). Compared to the time period in the second period calculated using the packet, it is possible to estimate the state of traffic and the like of the communication network 130 in the first period, further using the time synchronization in the first period It is possible to determine whether to synchronize the time of the slave device using a packet.

Meanwhile, the above-described embodiments of the present invention can be written as a program that can be executed in a computer, and can be implemented in a computer that operates the program using a computer-readable recording medium.

The program may be a program implemented in a high-level language code that may be executed in a computer using an interpreter, as well as a program implemented in machine code generated by a compiler.

In addition, the computer-readable recording medium may include any storage medium such as a magnetic storage medium (for example, a ROM, a floppy disk, a hard disk, etc.), an optical reading medium (for example, a CD-ROM, a DVD, etc.). do.

In addition, the computer is not limited to a personal computer (PC) or a notebook computer, but is provided with a central processing unit (CPU) such as a server, a smart phone, a tablet PC, a PDA, a mobile phone, and any information processing capable of executing a computer program. Device.

In addition, FIG. 6 illustrates a configuration diagram of a time-synchronous slave device 120 apparatus according to an embodiment of the present invention. As can be seen in FIG. 6, the time-synchronizing slave device 120 apparatus according to an embodiment of the present invention is a slave device 120 apparatus that synchronizes time between devices connected to the communication network 130. The packet receiver 122, the second packet receiver 124, the first period calculator 126, and the time synchronizer 128 may be configured.

Hereinafter, the apparatus of the time-synchronizing slave device 120 according to an embodiment of the present invention will be described in detail with reference to FIGS. 3 and 6.

First, the first packet receiver 122 receives a first time synchronization packet in a first period k from the master device 110.

Referring to FIG. 3, the master device 110 transmits a Sync (k) packet to the slave device 120 through the communication network 130 at a predetermined time t _{k, 1} . At this time, the first packet receiver 122 receives the Sync (k) packet and records the time point (t _{k, 2} ) at which it was received. Subsequently, the slave device 120 may further exchange a series of packets to calculate a time offset with the master device 110 (Follow_up (k), Delay_Req (k), Delay_Resp (k) packets. Etc).

Next, the second packet receiving unit 124 receives the second time synchronization packet in the second period transmitted after a predetermined time period has elapsed from the master device 110. Referring to FIG. 3, the master device 110 transmits a Sync (k + 1) packet to the slave device 120 through the communication network 130 after a predetermined time period T _k elapses. Accordingly, the second packet receiver 124 receives the Sync (k + 1) packet and records the time point (t _{k + 1,2} ) at which it was received. In addition, the slave device 120 may further exchange a series of packets to calculate a time offset with the master device 110 (Follow_up (k + 1), Delay_Req (k + 1), Delay_Resp). (k + 1) packets, etc.).

In FIG. 6, the first packet receiver 122 and the second packet receiver 124 are illustrated as separate components. However, this is only an exemplary embodiment according to functional division, and the first packet receiver 122 and the first packet receiver 122 are illustrated in FIG. The second packet receiver 124 may be implemented to use one communication module in common, or may be implemented as one module.

Next, the first period calculator 126 calculates a time period for the first period using the reception time of the first time synchronization packet and the reception time of the second time synchronization packet. In the case of FIG. 3, the reception time t _{k, 2 of} the first time synchronization packet Sync (k) and the reception time t _{k + of} the second time synchronization packet Sync (k + 1) measured above. _1,2 ) to calculate a time period T? = T _{k + 1,2} -t _{k, 2} for the first period.

Finally, the time synchronizer 128 synchronizes the time of the slave device 120 using the first time synchronization packet in consideration of the time period calculated for the first period.

Further, the time synchronizer 128 estimates a communication state such as traffic of the communication network 130 in the first period in consideration of the time period calculated for the first period (not shown). And a time synchronizer (not shown) for synchronizing the time of the slave device 120 using the first time synchronization packet in consideration of the state of the communication network 130 in the first period. It may be.

More specifically, the time synchronization unit 128 does not use the first time synchronization packet for time synchronization with respect to the slave device 120 when the state of the communication network 130 does not reach a predetermined reference value. In addition, the first time synchronization packet may be weighted according to the communication network 130 state to be used for time synchronization with respect to the slave device 120.

Furthermore, the apparatus of time synchronization slave device 120 according to an embodiment of the present invention receives a third time synchronization packet in a third period transmitted after a predetermined time period elapses from the master device 110. A third packet receiver (not shown), a second period calculator (not shown) that calculates a time period for the second period by using a reception time of the second time synchronization packet and a reception time of the third time synchronization packet. And a communication network state estimator (not shown) for estimating the state of the communication network 130 in the first period by comparing the time period calculated for the first period and the time period calculated for the second period. It may further include.

That is, the time period in the first period k is calculated using the time synchronization packet in the first period k, and further, this is the time synchronization in the second period (ie, another period such as k + 1). Compared to the time period in the second period calculated using the packet, it is possible to estimate the state of traffic and the like of the communication network 130 in the first period, further using the time synchronization in the first period It is possible to determine whether to synchronize the time of the slave device using a packet.

The above description is merely illustrative of the technical idea of the present invention, and those skilled in the art to which the present invention pertains may various modifications and changes without departing from the essential characteristics of the present invention. Therefore, the embodiments described in the present invention are not intended to limit the technical spirit of the present invention but to describe the present invention, and are not limited to these embodiments. The protection scope of the present invention should be interpreted by the following claims, and all technical ideas within the equivalent scope should be interpreted as being included in the scope of the present invention.

100: visual synchronization system
110: master device
120, 120a, 120n: slave device
122: first packet receiver
124: second packet receiving unit
126: first cycle calculator
128: time synchronization unit
130: communication network

Claims (10)

A method of synchronizing time between devices connected to a communication network,
A first packet transmission step of receiving, by the slave device, a first time synchronization packet in a first period of time synchronization packets transmitted at a predetermined time period T from the master device;
A second packet transmission step of receiving, by the slave device, a second time synchronization packet in a second period transmitted after the predetermined time period (T) has passed from the master device;
A first period calculating step of calculating a time period calculation value T 'for the first period by using a difference between a reception time of the first time synchronization packet and a reception time of the second time synchronization packet; And
Time synchronization for synchronizing the time of the slave device using the first time synchronization packet in consideration of the communication network state for the first period estimated from the time period calculation value T 'calculated for the first period. And a step comprising the steps of time synchronization. delete The method of claim 1,
In the time synchronization step,
When the communication network state does not reach a predetermined reference value,
Do not use the first time synchronization packet for time synchronization for the slave device, or
And assigning a weight to the first time synchronization packet according to the communication network state to use the time synchronization for the slave device. The method of claim 1,
A third packet transmission step of receiving, by the slave device, a third time synchronization packet in a third period transmitted after the predetermined time period (T) has elapsed from the master device;
A second period calculating step of calculating a time period calculation value T 'for the second period by using a difference between a reception time of the second time synchronization packet and a reception time of the third time synchronization packet; And
Estimating a communication network state in the first period by comparing the time period calculation value T 'calculated for the first period and the time period calculation value T' calculated for the second period. Time synchronization method characterized in that. A program stored in a computer readable medium for executing the method according to any one of claims 1 to 3 on a computer. A slave device apparatus for synchronizing time between devices connected to a communication network,
A first packet receiver configured to receive a first time synchronization packet in a first period among time synchronization packets transmitted at a predetermined time period T from the master device;
A second packet receiver configured to receive a second time synchronization packet in a second period transmitted after the predetermined time period T passes from the master device;
A first period calculator configured to calculate a time period calculation value T ′ for the first period by using a difference between a reception time of the first time synchronization packet and a reception time of the second time synchronization packet; And
Time synchronization for synchronizing the time of the slave device using the first time synchronization packet in consideration of the communication network state for the first period estimated from the time period calculation value T 'calculated for the first period. Slave device apparatus comprising a. delete The method of claim 6,
In the time synchronization unit,
When the communication network state does not reach a predetermined reference value,
Do not use the first time synchronization packet for time synchronization for the slave device, or
And the first time synchronization packet is weighted according to the communication network state to be used for time synchronization with the slave device. The method of claim 6,
A third packet receiver configured to receive a third time synchronization packet in a third period transmitted after the predetermined time period T has elapsed from the master device;
A second period calculator configured to calculate a time period calculation value T ′ for the second period by using a difference between a reception time of the second time synchronization packet and a reception time of the third time synchronization packet; And
A communication network state estimation for estimating a communication network state in the first period by comparing the time period calculated value T 'calculated for the first period and the time period calculated value T' calculated for the second period The slave device device further comprises. A time synchronization system for synchronizing time between devices connected to a communication network,
After transmitting the first time synchronization packet in the first period of the time synchronization packets transmitted every predetermined time period T,
A master device for transmitting a second time synchronization packet in a second period after the predetermined time period T has elapsed; And
Receiving the first time synchronization packet in the first period from the master device,
After receiving the second time synchronization packet in the second period,
Calculating a time period calculation value T ′ for the first period by using a difference between a reception time of the first time synchronization packet and a reception time of the second time synchronization packet,
Slave for synchronizing the time for the master device using the first time synchronization packet in consideration of the communication network state for the first period estimated from the time period calculation value T 'calculated for the first period. And a device.

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