MEASURING DEVICE, MEASURING METHOD, AND TIME SYNCHRONIZATION SYSTEM

A measurement instrument (30) according to the present disclosure includes: a UTC acquisition unit (31) configured to acquire a reference time from a satellite signal; a BC time acquisition unit (32) configured to acquire time information regarding an in-device time of a first device (3); a UTC-BC offset calculation processing unit (33) configured to calculate a first offset that is a difference between the reference time and the in-device time of the first device (3) based on the reference time and the time information; a BC-client offset calculation processing unit (34) configured to acquire a copy of the packet and calculate a second offset that is a difference between the in-device time of the first device (3) and the in-device time of the second device (4) based on the acquired packet and a transmission delay between the first device (3) and the second device (4); and a time accuracy calculation processing unit (35) configured to measure accuracy of an in-device time of the second device (4) with respect to the reference time based on the first and second offsets.

TECHNICAL FIELD

The present disclosure relates to a measurement instrument, a measurement method, and a time synchronization system.

BACKGROUND ART

A precision time protocol (PTP) defined by the IEEE-1588 standard is a protocol that synchronizes a time (in-device time) of a computer on a local area network (LAN) with high accuracy (see Non Patent Literature 1).FIG.10is a diagram illustrating an exemplary configuration of a conventional time synchronization system1athat synchronizes times of devices on a network using a PTP protocol.

A time synchronization system1aillustrated inFIG.10includes a grand master clock100, a client device200, and a measurement instrument300. The grand master clock100and the client device200can communicate with each other via the network2such as a LAN.

The grand master clock100includes a global navigation satellite system (GNSS) antenna that receives a signal (GNSS signal) from a satellite of a GNSS such as the Global Positioning System (GPS). The grand master clock100receives a GNSS signal via a GNSS antenna, and acquires universal time coordinated (UTC) from the received GNSS signal. The grand master clock100has a master function of delivering the acquired UTC as a reference time via the network2.

The client device200has a slave function of synchronizing an in-device time with a time delivered from a device that has a master function. In the time synchronization system1aillustrated inFIG.10, the grand master clock100is a device that has a master function, and the client device200synchronizes the in-device time with the time delivered from the grand master clock100. The client device200is, for example, a base station device in a mobile phone network.

As a measurement method of measuring accuracy of the in-device time of the client device200, as illustrated inFIG.10, there is a method in which a measurement instrument300synchronized with the GNSS (synchronized with the time delivered by the GNSS) is connected to the client device200, and signal quality of a timing reference signal such as a 1 pulse per second (PPS) signal output by the client device200is compared with a time delivered by the GNSS (for example, see Non Patent Literature 2.). The 1PPS signal is a signal output at one pulse per second. The 1PPS signal is input from the client device200to the measurement instrument300, for example, by connecting the client device200to the measurement instrument300by a coaxial cable. Therefore, it is necessary install the client device200and the measurement instrument300in a range in which connection by a coaxial cable is possible, for example, in the same building or the like.

CITATION LIST

Non Patent Literature

Non Patent Literature 1: IEEE Std 1588™-2019 “IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems”

SUMMARY OF INVENTION

Technical Problem

In the measurement method of the related art described with reference toFIG.10, there arises a constraint that a GNSS antenna capable of receiving a GNSS signal is required at a measurement location, or a constraint that the GNSS signal is received for a sufficient time in advance, the measurement instrument300synchronized with the GNSS is carried to the measurement location while the synchronization is lost, and it is necessary to perform measurement. Therefore, in the measurement method of the related art, there is a problem that preliminary environmental maintenance and a large amount of human operation are required in order to measure accuracy of an in-device time. There is a problem that measurement may be difficult due to a constraint that a GNSS antenna is required or a constraint that it is necessary to perform measurement while synchronization of the measurement instrument300is lost.

An object of the present disclosure made in view of the above-described problems is to provide a measurement instrument, a measurement method, and a time synchronization system capable of relaxing the above-described constraints and measuring the accuracy of the in-device time more simply.

Solution to Problem

In order to solve the foregoing problem, a measurement instrument according to an aspect of the present disclosure is a measurement instrument that measures accuracy of an in-device time of a second device with respect to a reference time in the second device that synchronizes the in-device time with the reference time and synchronizes the in-device time with a first device by transmitting and receiving a packet to and from the first device that delivers the in-device time. The measurement instrument includes: a first acquisition unit configured to acquire the reference time from a satellite signal; a second acquisition unit configured to acquire time information regarding an in-device time of the first device; a first calculation processing unit configured to calculate a first offset that is a difference between the reference time and the in-device time of the first device based on the reference time acquired by the first acquisition unit and the time information acquired by the second acquisition unit; a second calculation processing unit configured to acquire a copy of the packet transmitted and received between the first and second devices, and calculate a second offset that is a difference between the in-device time of the first device and the in-device time of the second device based on the acquired packet and a transmission delay between the first and second devices; and a third calculation processing unit configured to measure accuracy of the in-device time of the second device with respect to the reference time based on the first and second offsets.

In order to solve the above problem, a measurement method according to another aspect of the present disclosure is a measurement method by a measurement instrument that measures accuracy of an in-device time of a second device with respect to a reference time in the second device that synchronizes the in-device time with the reference time and synchronizes the in-device time with a first device by transmitting and receiving a packet to and from the first device that delivers the in-device time. The measurement method includes: a step of acquiring the reference time from a satellite signal; a step of acquiring time information regarding an in-device time of the first device; a step of calculating a first offset that is a difference between the reference time and the in-device time of the first device based on the acquired reference time and the acquired time information; a step of acquiring a copy of the packet transmitted and received between the first and second devices, and calculating a second offset that is a difference between the in-device time of the first device and the in-device time of the second device based on the acquired packet and a transmission delay between the first and second devices; and a step of measuring accuracy of the in-device time of the second device with respect to the reference time based on the first and second offsets.

In order to solve the above problem, a time synchronization system according to still another aspect of the present disclosure is a time synchronization system including: a first device configured to synchronize an in-device time with a reference time and deliver the in-device time;a second device configured to synchronize an in-device time with the first device by transmitting and receiving a packet to and from the first device; and a measurement instrument configured to measure accuracy of an in-device time of the second device with respect to the reference time in the second device. The measurement instrument includes: a first acquisition unit configured to acquire the reference time from a satellite signal; a second acquisition unit configured to acquire time information regarding an in-device time of the first device; a first calculation processing unit configured to calculate a first offset that is a difference between the reference time and the in-device time of the first device based on the reference time acquired by the first acquisition unit and the time information acquired by the second acquisition unit; a second calculation processing unit configured to acquire a copy of the packet transmitted and received between the first and second devices, and calculate a second offset that is a difference between the in-device time of the first device and the in-device time of the second device based on the acquired packet and a transmission delay between the first and second devices; and a third calculation processing unit configured to measure accuracy of the in-device time of the second device with respect to the reference time based on the first and second offsets.

Advantageous Effects of Invention

According to the measurement instrument, the measurement method, and the time synchronization system according to the present disclosure, it is possible to more easily measure accuracy of an in-device time.

DESCRIPTION OF EMBODIMENTS

First, an overview of a measurement instrument30according to the present disclosure will be described with reference toFIG.1.

The measurement instrument30according to the present disclosure is a device that measures accuracy of an in-device time of a second device4with respect to a reference time in the second device4that synchronizes the in-device time with a first device3by transmitting and receiving a PTP packet to and from the first device3. The first device3is a device that has a master function of synchronizing an in-device time with a reference time (UTC or a time delivered from another device) and delivering the in-device time. The other device is a device that is provided above the first device3and has a master function. The second device4is a device that has a slave function of synchronizing an in-device time with a time delivered from the first device3that has a master function.

The measurement instrument30acquires a copy of the PTP packet transmitted and received between the first device3and the second device4. Accordingly, in the present embodiment, in order to copy mutual communication (both upstream and downstream communication) between the first device3and the second device4, a copy point for copying a PTP packet is provided between the first device3and the second device4. The measurement instrument30acquires a copy of the PTP packet via the copy point. Hereinafter, acquisition of a copy of the PTP packet by the measurement instrument30via the copy point is simply described as “acquisition of the PTP packet” in some cases.

The measurement instrument30acquires time information regarding an in-device time of the first device3. The measurement instrument30acquires a GNSS signal through a GNSS antenna and acquires a reference time (UTC) from the acquired GNSS signal. The measurement instrument30measures accuracy of the in-device time of the second device4with respect to the reference time based on the acquired PTP packet, the reference time, and the time information.

The measurement instrument30acquires a copy of the PTP packet and measures the accuracy of the in-device time of the second device4with respect to the reference time using the acquired PTP packet. Then, it is not necessary to carry the measurement instrument30to an installation location of the second device4when measurement is performed. It is possible to alleviate a constraint such as bringing of the measurement instrument300synchronized with the installation location of the GNSS antenna and the reference time as in the time synchronization system1aof the related art. Therefore, the measurement instrument30according to the present disclosure can measure the accuracy of the in-device time more easily. The measurement instrument30according to the present disclosure remotely measure the accuracy of the in-device time of the second device4. Therefore, it is possible to promptly perform maintenance countermeasures when the time error occurs.

Note that, in the present disclosure, it is sufficient that the first device3that has the master function and the second device4that has the slave function can transmit and receive the PTP packet. Therefore, there is no constraint that the first device3and the second device4are installed in the same building.

Further, the constraint of the installation positions of the first device3and the measurement instrument30varies depending on a method of acquiring the time information. When the measurement instrument30acquires the time information from a 1PPS signal output from the first device3to be described below, it is necessary to connect the first device3to the measurement instrument30by a coaxial cable. Therefore, it is necessary to install the first device3and the measurement instrument30in a range in which the first device3and the measurement instrument30can be connected by a coaxial cable, for example, in a range within tens of meters. When the measurement instrument30acquires the time information from the PTP packet output from the first device3to be described below, it is sufficient that the first device3and the measurement instrument30can transmit and receive the PTP packet. Therefore, there is no constraint that the first device3and the measurement instrument30are installed in the same building.

In the present disclosure, it is sufficient that the measurement instrument30may copy and acquire the PTP packet transmitted and received between the first device3and the second device4. Therefore, there is no constraint that the second device4and the measurement instrument30are installed in the same building.

Next, a configuration of the time synchronization system1according to the present embodiment will be described with reference toFIG.2.

As illustrated inFIG.2, the time synchronization system1according to the present embodiment includes a boundary clock10, a client device20, and a measurement instrument30.

The boundary clock10functions as a device that has a slave function with respect to a superordinate device that has a master function and functions as a device that has a master function with respect to a subordinate device that has a slave function. In the present embodiment, the boundary clock10functions as a device that has a slave function with respect to the grand master clock100, and functions as a device that has a master function with respect to the client device20. Therefore, the boundary clock10synchronizes the in-device time of the boundary clock10with the time (the reference time) delivered from the grand master clock100by transmitting and receiving the PTP packet to and from the grand master clock100. The boundary clock10delivers the in-device time to the client device20by transmitting and receiving the PTP packet to and from the client device20. The boundary clock10outputs a pulse signal (1PPS signal) to the measurement instrument30at 1PPS in synchronization with the in-device time of the boundary clock10as time information regarding the in-device time of the boundary clock10. The boundary clock10calculates a packet transmission delay with the client device20and outputs a calculation result of the transmission delay to the measurement instrument30.

The client device20synchronizes the in-device time with the time delivered from the boundary clock10by transmitting and receiving the PTP packet to and from the boundary clock10. Accordingly, in the time synchronization system illustrated inFIG.2, the boundary clock10corresponds to the first device3that has the master function, and the client device20corresponds to the second device4that has the slave function.

The measurement instrument30measures the accuracy of the in-device time with respect to the reference time in the client device20as the second device4. The measurement instrument30acquires a copy of the PTP packet transmitted and received between the boundary clock10and the client device20. The measurement instrument30measures an error of the accuracy of the in-device time with respect to the reference time in the client device20based on the acquired PTP packet, the 1PPS signal, and the transmission delay between the boundary clock10and the client device20.

Next, configurations of the boundary clock10, the client device20, and the measurement instrument30will be described with reference toFIG.2. First, the configuration of the boundary clock10will be described.

As illustrated inFIG.2, the boundary clock10includes packet transceiver units11and12, a time synchronization processing unit13, a 1PPS transmission unit14, a transmission delay measurement packet transceiver unit15, and a transmission delay calculation processing unit16.

The packet transceiver unit11transmits and receives the PTP packet to and from the grand master clock100. The packet transceiver unit12transmits and receives the PTP packet to and from the client device20.

The time synchronization processing unit13acquires the time delivered by the grand master clock100from the PTP packet acquired from the grand master clock100via the packet transceiver unit11, and synchronizes the in-device time of the boundary clock10with the acquired time.

The 1PPS transmission unit14outputs the pulse signal (the 1PPS signal) to measurement instrument30at 1PPS in synchronization with the in-device time of the boundary clock10.

The transmission delay measurement packet transceiver unit15transmits and receives a packet (a transmission delay measurement packet) for measuring a transmission delay between the boundary clock10and the client device20to and from the client device20.

The transmission delay calculation processing unit16calculates a transmission delay between the boundary clock10and the client device20from the transmission delay measurement packets transmitted and received by the transmission delay measurement packet transceiver unit15. The transmission delay calculation processing unit16outputs a calculation result of the transmission delay to the measurement instrument30.

First, the configuration of the client device20will be described.

As illustrated inFIG.2, the client device20includes a packet transceiver unit21, a time synchronization processing unit22, a transmission delay measurement packet transceiver unit23, and a transmission delay calculation processing unit24.

The packet transceiver unit21transmits and receives the PTP packet to and from the boundary clock10.

The time synchronization processing unit22acquires the time delivered by the boundary clock10from the PTP packet received from the boundary clock10via the packet transceiver unit21, and synchronizes the in-device time of the client device20with the acquired time.

The transmission delay measurement packet transceiver unit23transmits and receives the transmission delay measurement packet to and from the boundary clock10.

A transmission delay between boundary clock10and the client device20is calculated from the transmission delay measurement packets transmitted and received by the transmission delay calculation processing unit24and the transmission delay measurement packet transceiver unit23.

Next, a configuration of the measurement instrument30will be described.

As illustrated inFIG.2, the measurement instrument30includes a UTC acquisition unit31, a BC time acquisition unit32, a UTC-BC offset calculation processing unit33, a BC-client offset calculation processing unit34, and a time accuracy calculation processing unit35.

The UTC acquisition unit31serving as a first acquisition unit receives a GNSS signal that is a satellite signal transmitted from a GNSS satellite via a GNSS antenna. The UTC acquisition unit31acquires a reference time (UTC) from the received GNSS signal and synchronizes the in-device time of the measurement instrument30with the acquired time. The UTC acquisition unit31outputs the obtained time to the UTC-BC offset calculation processing unit33.

The BC time acquisition unit32serving as a second acquisition unit acquires time information regarding the in-device time of the boundary clock10. In the present embodiment, the BC time acquisition unit32acquires a 1PPS signal that is a pulse signal output from the boundary clock10at 1PPS in synchronization with the in-device time of the boundary clock10, and acquires time information regarding the in-device time of the boundary clock10from the acquired 1PPS signal. The BC time acquisition unit32outputs the acquired in-device time of the boundary clock10to the UTC-BC offset calculation processing unit33.

The UTC-BC offset calculation processing unit33serving as a first calculation processing unit calculates a first offset that is a difference between UTC and the in-device time of the boundary clock10based on the reference time (UTC) acquired by the UTC acquisition unit31and the in-device time of the boundary clock10acquired by the BC time acquisition unit32. The UTC-BC offset calculation processing unit33outputs the calculated first offset to the time accuracy calculation processing unit35.

The BC-client offset calculation processing unit34serving as a second calculation processing unit acquires a copy of the PTP packet transmitted and received between the boundary clock10and the client device20. The BC-client offset calculation processing unit34calculates a second offset which is a difference between the in-device time of the boundary clock10and the in-device time of the client device20based on the acquired PTP packet and the transmission delay between the boundary clock10and the client device20. The BC-client offset calculation processing unit34outputs the calculated second offset to the time accuracy calculation processing unit35.

The time accuracy calculation processing unit35serving as a third calculation processing unit measures the accuracy of the in-device time of the client device20with respect to the reference time (UTC) based on the first offset calculated by the UTC-BC offset calculation processing unit33and the second offset calculated by the BC-client offset calculation processing unit34.

The measurement instrument30acquires the PTP packet and measures the accuracy of the in-device time of the client device20with respect to the reference time using the acquired PTP packet, and thus it is not necessary to carry the measurement instrument30to the installation location of the client device20when measurement is performed. It is possible to alleviate a constraint such as bringing of the measurement instrument300synchronized with the installation location of the GNSS antenna and the reference time as in the time synchronization system1aof the related art. Therefore, the measurement instrument30according to the present disclosure can measure the accuracy of the in-device time more easily. Furthermore, the measurement instrument30according to the present disclosure can remotely measure the accuracy of the in-device time of the client device20. Therefore, it is possible to promptly perform maintenance countermeasures when a time error occurs.

InFIG.2, an example in which the boundary clock10is the first device3and the client device20is the second device4has been described, but the present disclosure is not limited thereto. For example, the grand master clock100that has the master function may be the first device3, the boundary clock10that has the slave function may be the second device4, and the measurement instrument30may measure the accuracy of the in-device time in the boundary clock10.

Next, an operation of the measurement instrument30according to the present embodiment will be described.

FIG.3is a flowchart illustrating an example of an operation of the measurement instrument30according to the present embodiment and is a diagram illustrating a measurement method by the measurement instrument30.

The UTC acquisition unit31acquires a reference time (UTC) from a GNSS signal received from a satellite via the GNSS antenna (step S11).

The BC time acquisition unit32acquires time information regarding the in-device time of boundary clock10serving as the first device3(step S12). In the time synchronization system1illustrated inFIG.2, the BC time acquisition unit32acquires time information from the 1PPS signal output from the boundary clock10.

The UTC-BC offset calculation processing unit33calculates a first offset that is a difference between the reference time and the in-device time of boundary clock10based on the reference time (UTC) acquired by the UTC acquisition unit31and the time information acquired by the BC time acquisition unit32(step S13). Hereinafter, it is assumed that the first offset is X seconds.

The BC-client offset calculation processing unit34acquires a copy of the PTP packet transmitted and received between the boundary clock10and the client device20. The BC-client offset calculation processing unit34calculates the second offset which is a difference between the in-device time of the boundary clock10and the in-device time of the client device20based on the acquired PTP packet and the transmission delay between the boundary clock10and the client device20(step S14). Hereinafter, it is assumed that the second offset is Y seconds. Details of the calculation of the second offset will be described below.

InFIG.3, the processes from steps S11to S13and the process of step S14are illustrated as being branched. Actually, these processes are not branched and are sequentially performed.

The time accuracy calculation processing unit35measures the accuracy of the in-device time of the client device20with respect to the reference time based on the first offset calculated by the UTC-BC offset calculation processing unit33and the second offset calculated by the BC-client offset calculation processing unit34(step S15). For example, the time accuracy calculation processing unit35calculates a difference (offset) between the reference time and the in-device time of the client device20as the accuracy of the in-device time of the client device20with respect to the reference time. Specifically, the time accuracy calculation processing unit35calculates the offset between the reference time and the in-device time of the client device20by the sum (X+Y) of the first offset (X seconds) and the second offset (Y seconds).

Next, calculation of the second offset by the BC-client offset calculation processing unit34will be described with reference toFIG.4.

First, a message transmitted and received between the boundary clock10and the client device20according to the PTP will be described. A message transmitted and received between the boundary clock10and the client device20includes one or a plurality of PTP packets.

As illustrated inFIG.4, the boundary clock10first transmits a Sync message to the client device20(step S21). The boundary clock10includes a timestamp indicating time T1(first time), which is the transmission time of the Sync message, in the Sync message and transmits the Sync message to the client device20.

When receiving the Sync message transmitted from the boundary clock10at time T2(second time), the client device20transmits Delay_Req message to the boundary clock10at time T3in response to the Sync message (step S22). The client device20includes a timestamp indicating time T3(third time) which is the transmission time of the Delay_Req message in the Delay_Req message and transmits the Delay_Req message to the boundary clock10.

When the Delay_Req message transmitted from the client device20is received at time T4, the boundary clock10transmits a Delay_Resp message to the client device20in response to the Delay_Req message (step S23). The boundary clock10includes a timestamp indicating time T4(fourth time), which is the reception time of the Delay_Req message in the Delay_Resp message, and transmits the resulting Delay_Resp message to the client device20.

The BC-client offset calculation processing unit34acquires the PTP packet in which the message transmitted and received between the boundary clock10and the client device20is copied at a copy point between the boundary clock10and the client device20.

That is, the BC-client offset calculation processing unit34acquires the PTP packet P1(first packet) obtained by copying the PTP packet included in the Sync message. The PTP packet P1is a packet transmitted from the boundary clock10serving as the first device3to the client device20serving as the second device4, and includes time T1(first time) which is a transmission time of the packet.

The BC-client offset calculation processing unit34acquires the PTP packet P2(second packet) included in the Delay_Req message. The PTP packet P2is a packet transmitted from the client device20serving as the second device4to the boundary clock10serving as the first device3and is a packet including time T3(third time) which is a transmission time of the packet.

The BC-client offset calculation processing unit34acquires the PTP packet P3(third packet) included in the Delay_Resp message. The PTP packet P3is a packet transmitted from the boundary clock10serving as the first device3to the client device20serving as the second device4, and is a packet including time T4(fourth time) which is a reception time of the PTP packet P2(second packet) included in the Delay_Req message.

The BC-client offset calculation processing unit34acquires time T1from the acquired PTP packet P1. The BC-client offset calculation processing unit34acquires time T3from the acquired PTP packet P2. The BC-client offset calculation processing unit34acquires time T4from the acquired PTP packet P3.

The BC-client offset calculation processing unit34calculates the second offset by the following Expression (1) based on times T1to T4.

As described above, the BC-client offset calculation processing unit34can receive times T1, T3, and T4from the copy of the acquired PTP packet. However, since time T2which is the reception time of the Sync message by the client device20cannot be acquired from the PTP packet, it is necessary for the BC-client offset calculation processing unit34to separately acquire time T2. As a method of acquiring time T2, there is a method of using a transmission delay between the boundary clock10and the client device20. The transmission delay between the boundary clock10and the client device20is calculated by the transmission delay calculation processing unit16by transmitting and receiving the transmission delay measurement packet between the boundary clock10and the client device20. Hereinafter, the calculation of the transmission delay by the transmission delay calculation processing unit16will be described below with reference toFIG.5.

InFIG.5, a method in which Ethernet (registered trademark) delay measurement (ETH-DM) is used will be described. The ETH-DM is a delay measurement method defined in JT-Y 1731 OAM functions and mechanisms for Ethernet based networks. The ETH-DM includes two methods of 1WAY ETH-DM and 2WYA ETH-DM. Hereinafter, a case in which 2WAY ETH-DM is used will be described as an example.

As illustrated inFIG.5, the transmission delay measurement packet transceiver unit15of the boundary clock10transmits a DMM frame to the client device20(step S31). When the DMM frame is received, the transmission delay measurement packet transceiver unit23of the client device20transmits the DMR frame to the boundary clock10(step S32). Hereinafter, the transmission time of the DMM frame by the boundary clock10is referred to as Tx Time stampf, and the reception time of the DMM frame by the client device20is referred to as Rx Time stampf. The transmission time of the DMR frame by the client device20is Tx Time stampb, and the reception time of the DMR frame by the boundary clock10is Rx Time stampb. The client device20includes the reception time Rx Time stampf of the DMM frame and the transmission time Tx Time stampb of the DMR frame in the DMR frame and transmits the DMR frame to the boundary clock10.

The frame delay of ETH-DM (a time required for roundtrip between the boundary clock10and the client device20) can be calculated by the following Expression (2).

The transmission delay calculation processing unit16acquires Rx Time stampf and Tx Time stampb from the DMR frame received from the client device20. The transmission delay calculation processing unit16can acquire Tx Time stampf and Rx Time stampb from transmission of a DMM frame and reception of a DMR frame by the transmission delay measurement packet transceiver unit15. Accordingly, the transmission delay calculation processing unit16can calculate the frame delay by Expression (2). The transmission delay calculation processing unit16outputs a transmission result of the transmission delay (frame delay) to the measurement instrument30.

The roundtrip transmission delay of the PTP packet between the boundary clock10and the client device20can be calculated by the following Expression (3) using times T1to T4described with reference toFIG.4.

The BC-client offset calculation processing unit34can calculate time T2based on the transmission delay calculated by the transmission delay calculation processing unit16and Expression (3). Then, the BC-client offset calculation processing unit34calculates the second offset based on the following Expression (4).

The method of calculating the transmission delay described with reference toFIG.5is merely exemplary, and any method may be used as long as the transmission delay can be obtained.

FIG.6is a diagram illustrating an exemplary configuration of a time synchronization system1A according to another embodiment of the present disclosure. InFIG.6, the same constituents as those inFIG.2are denoted by the same reference numerals, and the description thereof will be omitted.

As illustrated inFIG.6, the time synchronization system1A includes a boundary clock10A, the client device20, and a measurement instrument30A. The time synchronization system1A illustrated inFIG.6is different from the time synchronization system1illustrated inFIG.2in that the boundary clock10and the measurement instrument30are changed to a boundary clock10A and a measurement instrument30A, respectively.

The boundary clock10A includes packet transceiver units11,12, and17, a time synchronization processing unit13, a transmission delay measurement packet transceiver unit15, and a transmission delay calculation processing unit16. The boundary clock10A illustrated inFIG.6is different from boundary clock10illustrated inFIG.2in that 1PPS transmission unit14is removed and the packet transceiver unit17is added.

The packet transceiver unit17transmits and receives a PTP packet to and from the measurement instrument30A.

The measurement instrument30A includes the UTC acquisition unit31, the BC time acquisition unit32A, the UTC-BC offset calculation processing unit33, the BC-client offset calculation processing unit34, the time accuracy calculation processing unit35, and a packet transceiver unit36. The measurement instrument30A illustrated inFIG.6is different from the measurement instrument30illustrated inFIG.2in that a packet transceiver unit36is added and that the BC time acquisition unit32is changed to a BC time acquisition unit32A.

The packet transceiver unit36transmits and receives a PTP packet to and from the boundary clock10A, and outputs the received PTP packet to the BC time acquisition unit32A.

The BC time acquisition unit32A acquires time information from the PTP packet output from the packet transceiver unit36. That is, the BC time acquisition unit32A serving as the second acquisition unit acquires the PTP packet including time information regarding the in-device time of the boundary clock10serving as the first device3from the boundary clock10and acquires the time information from the acquired PTP packet.

In this way, in the time synchronization system1A illustrated inFIG.6, the BC time acquisition unit32A acquires the time information from the PTP packet transmitted from the boundary clock10. In the time synchronization system1illustrated inFIG.2, the BC time acquisition unit32acquires time information from the 1PPS signal. Therefore, in the time synchronization system1, it is necessary to connect the measurement instrument30to the client device20by a coaxial cable for transmitting a 1PPS signal, and there is a constraint on an installation location of the measurement instrument30. On the other hand, in the time synchronization system1A illustrated inFIG.6, since it is sufficient that the PTP packet can be transmitted and received between the boundary clock10A and the measurement instrument30A, the constraint on the installation place of the measurement instrument30A is further relaxed, and the measurement can be performed more easily.

The other configurations and operations in the time synchronization system1A illustrated inFIG.6are similar to those of the time synchronization system1illustrated inFIG.2, and thus, description thereof is omitted.

Next, a configuration of a time synchronization system1B according to still another embodiment of the present disclosure will be described with reference toFIG.7.

A time synchronization system1B illustrated inFIG.7includes a boundary clock10A, a client device20, a measurement instrument30B, and a transparent clock40. The time synchronization system1B illustrated inFIG.7is different from the time synchronization system1A illustrated inFIG.6in that a measurement instrument30A is changed to a measurement instrument30B and a transparent clock40is added.

The transparent clock40serving as the third device is provided between the boundary clock10A serving as the first device3and the client device20serving as the second device4and relays the PTP packet between the boundary clock10and the client device20.

As illustrated inFIG.7, the transparent clock40includes packet transceiver units41and42, an intra-device relay delay processing unit43, transmission delay measurement packet transceiver units44and45, and a transmission delay calculation processing unit46.

The packet transceiver unit41transmits and receives a PTP packet to and from the boundary clock10A. The packet transceiver unit42transmits and receives a packet to and from the client device20.

The intra-device relay delay processing unit43measures the time required for the relay processing of the PTP packet in the transparent clock40, and notifies a distribution destination of the PTP packet.

The transmission delay measurement packet transceiver unit44transmits and receives a transmission delay measurement packet to and from the boundary clock10. The transmission delay measurement packet transceiver unit45transmits and receives the transmission delay measurement packet to and from the client device20.

The transmission delay calculation processing unit46calculates a transmission delay between the boundary clock10A and the transparent clock40based on the transmission delay measurement packet transmitted to and received from the boundary clock10A by the transmission delay measurement packet transceiver unit44. The transmission delay calculation processing unit46calculates a transmission delay between the client device20and the transparent clock40based on the transmission delay measurement packet transmitted to and received from the client device20by the transmission delay measurement packet transceiver unit45. That is, the transmission delay calculation processing unit46calculates a transmission delay between the boundary clock10A serving as the first device3and the transparent clock40(third device) and a transmission delay between the client device20serving as the second device4and the transparent clock40. The transmission delay calculation processing unit46outputs the calculation result of the transmission delay to the measurement instrument30B.

The measurement instrument30B includes the UTC acquisition unit31, the BC time acquisition unit32A, the UTC-BC offset calculation processing unit33, the BC-client offset calculation processing unit34B, the time accuracy calculation processing unit35, and the packet transceiver unit36. The measurement instrument30B illustrated inFIG.7is different from the measurement instrument30A illustrated inFIG.6in that the BC-client offset calculation processing unit34is changed to a BC-client offset calculation processing unit34B.

The BC-client offset calculation processing unit34B serving as the second calculation processing unit acquires calculation results of transmission delay between the boundary clock10A and the transparent clock40and the transmission delay between the client device20and the transparent clock40by the transmission delay calculation processing unit46. The BC-client offset calculation processing unit34B acquires a copy of the PTP packet transmitted and received between the transparent clock40and the client device20. The BC-client offset calculation processing unit34B calculates the second offset based on the acquired calculation result of the transmission delay and (a copy of) the PTP packet.

Next, calculation of the second offset by the BC-client offset calculation processing unit34B will be described with reference toFIG.8. As described with reference toFIG.4, the boundary clock10A first transmits a Sync message to the client device20(step S21). The boundary clock10A includes a timestamp indicating time T1(first time) in the Sync message and transmits the Sync message to the client device20. The Sync message is transmitted to the client device20via the transparent clock40.

When the Sync message is received at time T2(second time), the client device20transmits the Delay_Req message to the boundary clock10A at time T3in accordance with the Sync message (step S22). The client device20includes a timestamp indicating time T3(third time) which is the transmission time of the Delay_Req message in the Delay_Req message, and transmits the Delay_Req message to the boundary clock10A. The Delay_Req message is transmitted to the boundary clock10A via the transparent clock40.

When the Delay_Req message is received at time T4, the boundary clock10A transmits the Delay_Resp message to the client device20in accordance with the Delay_Req message (step S23). The boundary clock10A includes a timestamp indicating time T4(fourth time) in Delay_Resp message, and transmits the Delay_Resp message to the client device20.

Hereinafter, the reception time of the Sync message by the transparent clock40is denoted by dt1, and the transmission time of the Sync message is denoted by dt2. The reception time of the Delay_Req message by the transparent clock40is denoted by dt3, and the transmission time of the Delay_Req message is denoted by dt4.

The BC-client offset calculation processing unit34B acquires time T1and a relay delay time dt2-dt1from the PTP packet P1to which the PTP packet constituting the Sync message has been copied.

Subsequently, the BC-client offset calculation processing unit34B acquires time T3from the PTP packet P2to which the PTP packet included in the Delay_Req message has been copied.

Subsequently, the BC-client offset calculation processing unit34B acquires time T4from the PTP packet P3to which the PTP packet included in the Delay_Resp message has been copied. The BC-client offset calculation processing unit34B acquires a relay delay time dt4-dt3of the Delay_Req message in the transparent clock40from the PTP packet P3.

The BC-client offset calculation processing unit34B calculates the second offset by the following Expression (5) based on times T1to T4, the relay delay time dt2-dt1, and the relay delay time dt4-dt3.

A method of calculating the second offset by the BC-client offset calculation processing unit34B is not limited to the method in which the above-described Expression (5) is used. Another method of calculating the second offset by the BC-client offset calculation processing unit34B will be described. Hereinafter, a transmission delay time between the boundary clock10A and the transparent clock40is defined as pt1, and a transmission delay time between the transparent clock40and the client device20is defined as pt2.

As described with reference toFIG.8, the BC-client offset calculation processing unit34B acquires time T1, the relay delay time dt2-dt1, and the transmission delay time pt1from the PTP packet P1. The transmission delay time pt1can be measured in accordance with, for example, a peer-to-peer mechanism (P2P) method. The P2P method is a method of measuring a transmission delay time between devices physically connected by a cable.

The BC-client offset calculation processing unit34B calculates the second offset in accordance with the following Expression (6) based on times T1and T2, the relay delay time dt2-dt1, the transmission delay time pt1between the boundary clock10A and the transparent clock40, and the transmission delay time pt2between the transparent clock40and the client device20.

The BC-client offset calculation processing unit34B cannot acquire time T2and the transmission delay time pt2from the PTP packet. Therefore, in the case of using Expression (5), the BC-client offset calculation processing unit34B needs to separately acquire time T2. When Expression (6) is used, it is necessary for the BC-client offset calculation processing unit34B to separately acquire time T2and the transmission delay time pt2.

As a method by which the client device20acquires time T2, for example, there is a method using ETH-DM described with reference toFIG.5. By using ETH-DM, the transmission delay calculation processing unit46of the transparent clock40can calculate a frame delay (a time required for DMM frame to reciprocate between the transparent clock40and the client device20) between the transparent clock40and the client device20. The BC-client offset calculation processing unit34B can calculate time T2based on the frame delay calculated by the transmission delay calculation processing unit46.

As another method by which the client device20acquires time T2, there is a method using the PTP packet described with reference toFIG.4. FromFIG.4, the roundtrip transmission delay between the boundary clock10A and the client device20is expressed by the following Expression (7).

In Expression (7), times T1, T3, and T4, the relay delay time dt2-dt1, and the relay delay time dt4-dt3can be acquired from the PTP packet. The roundtrip transmission delay can be calculated by ETH-DM. Accordingly, the BC-client offset calculation processing unit34B can calculate time T2based on Expression (7) using times T1, T3, and T4, the relay delay time dt2-dt1and the relay delay time dt4-dt3acquired from the PTP packet, and the roundtrip transmission delay calculated by the ETH-DM.

As still another method of acquiring time T2by the client device20, there is a method using times T1and T2described with reference toFIG.4. The roundtrip transmission delay between the boundary clock10A and the client device20is expressed by the following Expression (8).

In Expression (8), T1and dt2-dt1can be obtained from the PTP packet. The roundtrip transmission delay can be calculated by ETH-DM. Accordingly, the BC-client offset calculation processing unit34B can calculate time T2based on Expression (8) using T1and dt2-dt1acquired from the PTP packet and the roundtrip transmission delay calculated by ETH-DM.

Next, a hardware configuration of the measurement instrument30according to the present disclosure will be described. In the following description, the measurement instrument30will be described as an example, but the same applies to the measurement instruments30A and30B.

FIG.9is a diagram illustrating an example of a hardware configuration of the measurement instrument30according to an embodiment of the present disclosure.FIG.9illustrates an example of a hardware configuration of the measurement instrument30when the measurement instrument30is configured with a computer capable of executing a program command. Here, the computer may be a general-purpose computer, a dedicated computer, a workstation, a personal computer (PC), an electronic note pad, or the like. The program command may be a program code, a code segment, or the like for executing a necessary task.

As illustrated inFIG.9, the measurement instrument30includes a processor310, a read only memory (ROM)320, a random access memory (RAM)330, a storage340, an input unit350, a display unit360, and a communication interface (I/F)370. These configurations are communicably connected via a bus390to be able to communicate with each other. Specifically, the processor310is a central processing unit (CPU), a micro processing unit (MPU), a graphics processing unit (GPU), a digital signal processor (DSP), a system on a chip (SoC), or the like and may be configured with the same type or different types of a plurality of processors.

The processor310is a controller that executes control of each configuration and various types of arithmetic processing. That is, the processor310reads the program from the ROM320or the storage340, and executes the program using the RAM330as a work area. The processor310performs control of each of the above-described configurations and various types of arithmetic processing according to a program stored in the ROM320or the storage340. In the present embodiment, the ROM120or the storage140stores a program causing a computer to function as the measurement instrument30according to the present disclosure. The program is read and executed by the processor310to implement each configuration of the measurement instrument30, that is, the UTC acquisition unit31, the BC time acquisition unit32, the UTC-BC offset calculation processing unit33, the BC-client offset calculation processing unit34, and the time accuracy calculation processing unit35.

The program may be provided in a form in which the program is stored in a non-transitory storage medium, such as a compact disk read only memory (CD-ROM), a digital versatile disk read only memory (DVD-ROM), and a universal serial bus (USB) memory. The program may be downloaded from an external device via a network.

The ROM320stores various programs and various types of data. The RAM330serving as a work area temporarily stores programs or data. The storage340includes a hard disk drive (HDD) or a solid state drive (SSD) and stores various programs including an operating system and various types of data.

The input unit350includes a pointing device such as a mouse and a keyboard and is used to perform various inputs.

The display unit360is, for example, a liquid crystal display and displays various types of information. A touch panel system may be adopted so that the display unit360can function as the input unit350.

The communication interface370is an interface communicating with another device such as an external device (not illustrated). For example, a standard such as Ethernet (registered trademark), FDDI, and Wi-Fi (registered trademark) is used.

A computer can be suitably used to function as each unit of the above-described measurement instrument30. Such a computer can be implemented by storing a program describing processing content for implementing the function of each unit of the measurement instrument30in a storage unit of the computer, and reading and executing the program by a processor of the computer. That is, the program can cause the computer to function as the above-described measurement instrument30. The program can be recorded in a non-transitory recording medium. The program can also be provided via a network.

With regard to the above embodiments, the following supplements will be further disclosed.

A measurement instrument that measures accuracy of an in-device time of a second device with respect to a reference time in the second device that synchronizes the in-device time with the reference time and synchronizes the in-device time with the first device by transmitting and receiving a packet to and from the first device that delivers the in-device time, the measurement instrument including a processor:wherein the processoracquires the reference time from a satellite signal,acquires time information regarding an in-device time of the first device,calculates a first offset that is a difference between the reference time and the in-device time of the first device based on the acquired reference time and the acquired time information acquired by the second acquisition unit,acquires a copy of the packet transmitted and received between the first and second devices, and calculates a second offset that is a difference between the in-device time of the first device and the in-device time of the second device based on the acquired packet and a transmission delay between the first and second devices, andmeasures accuracy of the in-device time of the second device with respect to the reference time based on the first and second offsets.

The measurement instrument according to Supplement 1, wherein the processor acquires copies of a first packet that is a packet transmitted from the first device to the second device and includes a first time which is a transmission time of the packet, a second packet that is a packet transmitted from the second device to the first device in accordance with the first packet and includes a third time which is a transmission time of the packet, and a third packet that is a packet transmitted from the first device to the second device in accordance with the second packet and includes a fourth time which is a reception time of the second packet by the first device, calculates a second time that is a reception time of the first packet by the second device based on the first time, the third time, and the fourth time included in the first to third packets and the transmission delay, and calculates the second offset based on the first time, the second time, the third time, and the fourth time.

The measurement instrument according to Supplement 1, wherein the processor acquires the time information based on a pulse signal output from the first device at 1PPS in synchronization with the in-device time of the first device.

The measurement instrument according to Supplement 1, wherein the processor acquires a packet including time information regarding the in-device time of the first device from the first device, and acquires the time information from the acquired packet.

The measurement instrument according to Supplement 1, whereinwherein a third device that relays the packet is provided between the first and second devices,wherein the third device calculates a transmission delay between the first and third devices and a transmission delay between the second and third devices; andwherein the processor calculates the second offset based on a calculation result of the third device.

A measurement method by a measurement instrument that measures accuracy of an in-device time of a second device with respect to a reference time in the second device that synchronizes the in-device time with the reference time and synchronizes the in-device time with the first device by transmitting and receiving a packet to and from the first device that delivers the in-device time, the measurement method comprising:a step of acquiring the reference time from a satellite signal;a step of acquiring time information regarding an in-device time of the first device;a step of calculating a first offset that is a difference between the reference time and the in-device time of the first device based on the acquired reference time and the acquired time information;a step of acquiring a copy of the packet transmitted and received between the first and second devices, and calculating a second offset that is a difference between the in-device time of the first device and the in-device time of the second device based on the acquired packet and a transmission delay between the first and second devices; anda step of measuring accuracy of the in-device time of the second device with respect to the reference time based on the first and second offsets.

A time synchronization system comprising:a first device configured to synchronize an in-device time with a reference time and deliver the in-device time;a second device configured to synchronize an in-device time with the first device by transmitting and receiving a packet to and from the first device; anda measurement instrument configured to measure accuracy of an in-device time of the second device with respect to the reference time in the second device,wherein the measurement instrument includes a processor:wherein the processoracquires the reference time from a satellite signal;a second acquisition unit configured to acquire time information regarding an in-device time of the first device;calculates a first offset that is a difference between the reference time and the in-device time of the first device based on the reference time acquired by the first acquisition unit and the time information acquired by the second acquisition unit;acquires a copy of the packet transmitted and received between the first and second devices, and calculates a second offset that is a difference between the in-device time of the first device and the in-device time of the second device based on the acquired packet and a transmission delay between the first and second devices; andmeasures accuracy of the in-device time of the second device with respect to the reference time based on the first and second offsets.

Although the above-described embodiments have been described as representative examples, it is apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present disclosure. Accordingly, it should not be understood that the present invention is limited by the above-described embodiments, and various modifications or changes can be made without departing from the scope of the claims. For example, a plurality of configuration blocks described in the configuration diagrams of the embodiments can be combined into one, or one configuration block can be divided.

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