Communications device, communications system and communications method

Abstract

A communication device (100a) acquires control data, which is the data included in a first packet received from a Grand Master Clock (1) and related to control of transmission / reception of the first packet, calculates a transmission delay time between the Grand Master Clock (1) and the communication device (100a), calculates a correctionField (CF) value on the basis of the transmission time of the first packet by the Grand Master Clock (1) as notified from the Grand Master Clock (1), the calculated transmission delay time, and the reception time of the first packet by the communication device (100a) that is synchronized with an other communication device (100b), rewrites the CF value included in the acquired control data overwriting it with the calculated CF value, and transmits the packet of a format predetermined with the other communication device (100b) and including the control data after rewriting the CF value to the other communication device (100b).

Description

COMMUNICATION DEVICE, COMMUNICATION SYSTEM, AND COMMUNICATION METHOD

[0001] The present disclosure relates to a communication device, a communication system, and a communication method.

[0002] The Precision Time Protocol (PTP) defined in the IEEE-1588 standard is a protocol for synchronizing the time (device internal time) of computers on a LAN (Local Area Network) with high precision (see Non-Patent Document 1). PTP is used in a variety of fields, including mobile and industrial applications (see Non-Patent Documents 2 and 3). Figures 7A and 7B are diagrams showing an example configuration of a time synchronization system 10A that uses PTP to synchronize the time of devices on a network.

[0003] As shown in FIGS. 7A and 7B, a time synchronization system 10A includes a Grand Master Clock 1 and a Client device 2.

[0004] The Grand Master Clock 1 includes a GNSS antenna 1a that receives signals (GNSS signals) from satellites of a Global Navigation Satellite System (GNSS) such as the Global Positioning System (GPS). The Grand Master Clock 1 receives the GNSS signals via the GNSS antenna 1a and acquires International Atomic Time (TAI) from the received GNSS signals. The Grand Master Clock 1 has a master function that distributes the acquired TAI as a reference time via a network.

[0005] The client device 2 has a slave function for synchronizing the internal time of the device with the time of a device having a master function. The client device 2 is a device used by a user, such as a base station device in a mobile phone network.

[0006] When synchronizing the Grand Master Clock 1 with the client devices 2, a relay device for relaying signals may be provided between the Grand Master Clock 1 and the client devices 2 depending on the distance between the Grand Master Clock 1 and the client devices 2 and the number of client devices 2 synchronized with the Grand Master Clock 1. Examples of relay devices used in PTP include the Boundary Clock 3 shown in Fig. 7A and the Transparent Clock 4 shown in Fig. 7B.

[0007] The Boundary Clock 3 shown in FIG. 7A functions as a device with slave functionality with respect to a higher-level device with master functionality, and as a device with master functionality with respect to a lower-level device with slave functionality. In the time synchronization system 10A shown in FIG. 7A, the Boundary Clock 3 functions as a device with slave functionality with respect to the Grand Master Clock 1, and as a device with master functionality with respect to the Client device 2. Specifically, the Boundary Clock 3 measures an offset, which is the difference between the internal time of the Grand Master Clock 1 and the internal time of its own device (the difference between the internal time of the device with master functionality and the internal time of the device with slave functionality), by transmitting and receiving PTP packets with the Grand Master Clock 1, and synchronizes the internal time of its own device with the time of the Grand Master Clock 1 (reference time) based on the measured offset. Furthermore, the Boundary Clock 3 synchronizes the internal time of the Client device 2 with the internal time of its own device by transmitting and receiving PTP packets with the Client device 2.

[0008] 7B forwards PTP packets received from Grand Master Clock 1 to Client device 2, and forwards PTP packets received from Client device 2 to Grand Master Clock 1. Transparent Clock 4 measures the time it takes for a PTP packet to pass through its own device, and writes the result into the PTP packet while forwarding it. In this way, the internal time of Client device 2 can be synchronized with the internal time of Grand Master Clock 1.

[0009] IEEE Std 1588-2019, IEEE Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control SystemsITU-T G.8275.1 / Y.1369.1, Precision time protocol telecom profile for phase / time synchronization with full timing support from the networkIEEE Std 802.1AS‐2020, IEEE Standard for Local and Metropolitan Area Networks -- Timing and Synchronization for Time-Sensitive Applications

[0010] In PTP, different formats called profiles are defined for each field of use, which have different required parameters and time information formats, and time synchronization cannot be achieved between different profiles.One of the reasons why time synchronization cannot be achieved between different profiles is the difference in the method of measuring transmission delay.

[0011] There are two methods for measuring delay in a time synchronization system 10A including a transparent clock 4 shown in Fig. 7B: an end-to-end (E2E) method and a peer-to-peer (P2P) method. Each method will be described below.

[0012] Fig. 8 is a sequence diagram showing an example of the operation of each device in the E2E method. In Fig. 8, the Master device is a device equipped with a Master function, and the Client device is a device equipped with a Client function. There are two PTP time distribution methods: a two-step method and a one-step method. Fig. 8 explains the case where the two-step method is used.

[0013] At time T1, the Master device transmits a Sync message to Transparent Clock 4. Messages transmitted and received between devices in PTP include a field called a correction field (CF), which contains a correction value used for time correction in the Client device (for example, a value obtained by adding the time it takes for a frame to pass through the device). The Master device sets CF in the Sync message to 0. In the following, unless otherwise specified, the value of CF is assumed to be 0.

[0014] When the Transparent Clock 4 receives a Sync message at time dt1, it transmits the received Sync message to the Client device at time dt2. The Transparent Clock 4 stores the reception time dt1 of the Sync message from the Master device and the transmission time dt2 of the Sync message to the Client device.

[0015] At time T2, the client device receives the Sync message sent from Transparent Clock 4. The client device stores the time T2 when the Sync message was received.

[0016] After transmitting the Sync message, the Master device transmits a Follow_Up message to Transparent Clock 4. The Master device includes the transmission time T1 of the Sync message in the Follow_Up message.

[0017] When the Transparent Clock 4 receives the Follow_Up message, it transmits the received Follow_Up message to the Client device. The Transparent Clock 4 sets the CF of the Follow_Up message to the processing time of the Sync message in the Transparent Clock 4 (=dt2-dt1).

[0018] At time T3, the client device transmits a Delay_Req message to Transparent Clock 4. The client device periodically transmits the Delay_Req message.

[0019] When the Transparent Clock 4 receives the Delay_Req message at time dt3, it transmits the received Delay_Req message to the Master device at time dt4. The Transparent Clock 4 stores the reception time dt3 of the Delay_Req message from the Client device and the transmission time dt4 of the Delay_Req message to the Master device.

[0020] The master device receives the Delay_Req message at time T4 and stores the time T4 at which the master device received the Delay_Req message.

[0021] When the Master device receives the Delay_Req message, it transmits a Delay_Resp message to Transparent Clock 4. The Master device includes the reception time T4 of the Delay_Req message in the Delay_Resp message.

[0022] When the Transparent Clock 4 receives the Delay_Resp message, it transmits the received Delay_Resp message to the Client device. The Transparent Clock 4 sets the processing time of the Delay_Req message in the Transparent Clock 4 (=dt4-dt3) in the CF of the Delay_Resp message.

[0023] The client device calculates the offset, which is the difference between the device time of the master device and the device time of the client device, using the following formula (1): Offset = ((T2 - T1 - (dt2 - dt1)) - (T4 - T3 - (dt4 - dt3))) / 2 Formula (1) Based on the following: Time T1 when the master device sent the Sync message; Time T2 when the client device received the Sync message; Time T3 when the client device sent the Delay_Req message; Time T4 when the master device received the Delay_Resp message; the processing time of the Sync message in Transparent Clock 4 set in the CF of the Follow_Up message (= dt2 - dt1); and the processing time of the Delay_Req message in Transparent Clock 4 set in the CF of the Delay_Resp message (= dt4 - dt3).

[0024] The client device can synchronize its internal time with the internal time of the master device by correcting the internal time based on the calculated offset.

[0025] 8, the case where the two-step method is used is explained, but in the case of the one-step method, the Follow_Up message is not used. In this case, the Sync message transmission time T1 and the Sync message processing time (= dt2 - dt1) in Transparent Clock 4, which were included in the Follow_Up message, can be included in the Sync message.

[0026] 9 is a sequence diagram showing an example of the operation of each device in the P2P system, in which the two-step system is used.

[0027] The transparent clock 4 transmits a Pdelay_Req message to the master device at time t1, and stores the time t1 at which the transparent clock 4 transmits the Pdelay_Req message to the master device.

[0028] The master device receives the Pdelay_Req message at time t2 and stores the time t2 when the master device receives the Pdelay_Req message.

[0029] Upon receiving the Pdelay_Req message, the Master device transmits a Pdelay_Resp message to Transparent Clock 4 at time t3. The Master device includes the time t2 at which the Pdelay_Req message was received in the Pdelay_Resp message. The Master device stores the time t3 at which the Pdelay_Resp message was transmitted to Transparent Clock 4.

[0030] After transmitting the Pdelay_Resp message, the Master device transmits a Pdelay_Resp_Follow_Up message to Transparent Clock 4. The Master device includes the time t3 at which the Pdelay_Resp message was transmitted to Transparent Clock 4 in the Pdelay_Resp_Follow_Up message.

[0031] The Transparent Clock 4 receives the Pdelay_Resp message at time t4. The Transparent Clock 4 stores the time t4 when the Pdelay_Resp message is received. The Transparent Clock 4 also receives the Pdelay_Resp_Follow_Up message. The Transparent Clock 4 calculates the transmission delay time pt1 between the Master device and the Transparent Clock 4 using the following equation (2) based on the time t1 when the Transparent Clock 4 transmits the Pdelay_Req message, the time t2 when the Master device receives the Pdelay_Req message contained in the Pdelay_Resp message, the time t3 when the Master device transmits the Pdelay_Resp message contained in the Pdelay_Resp_Follow_Up message, and the time t4 when the Transparent Clock 4 receives the Pdelay_Resp message.

[0032] At time t5, the client device transmits a Pdelay_Req message to the transparent clock 4. The client device stores the time t5 at which the Pdelay_Req message was transmitted to the transparent clock 4.

[0033] The Transparent Clock 4 receives the Pdelay_Req message at time t6 and stores the time t6 at which the Transparent Clock 4 receives the Pdelay_Req message.

[0034] When the Transparent Clock 4 receives the Pdelay_Req message, it transmits a Pdelay_Resp message to the client device at time t7. The Transparent Clock 4 includes the reception time t6 of the Pdelay_Req message in the Pdelay_Resp message. The Transparent Clock 4 stores the transmission time t7 of the Pdelay_Resp message to the client device.

[0035] After transmitting the Pdelay_Resp message, the Transparent Clock 4 transmits a Pdelay_Resp_Follow_Up message to the client device, and includes the time t7 at which the Pdelay_Resp message was transmitted to the client device in the Pdelay_Resp_Follow_Up message.

[0036] The client device receives the Pdelay_Resp message at time t8. The client device stores the time t8 when the Pdelay_Resp message is received. The client device also receives the Pdelay_Resp_Follow_Up message. The client device calculates the transmission delay time pt2 between Transparent Clock 4 and the client device using the following equation (3) based on the time t5 when the client device sends the Pdelay_Req message, the time t6 when the Transparent Clock 4 receives the Pdelay_Req message included in the Pdelay_Resp message, the time t7 when the Transparent Clock 4 sends the Pdelay_Resp message included in the Pdelay_Resp_Follow_Up message, and the time t8 when the client device receives the Pdelay_Resp message: pt2=((t6-t5)+(t8-t7)) / 2 Equation (3)

[0037] The Master device sends a Sync message to Transparent Clock 4 at time T1.

[0038] When the Transparent Clock 4 receives a Sync message at time dt1, it transmits the received Sync message to the Client device at time dt2. The Transparent Clock 4 stores the reception time dt1 of the Sync message from the Master device and the transmission time dt2 of the Sync message to the Client device.

[0039] The client device receives the Sync message sent from Transparent Clock 4 at time T2.

[0040] After transmitting the Sync message, the Master device transmits a Follow_Up message to Transparent Clock 4. The Master device includes the transmission time T1 of the Sync message to Transparent Clock 4 in the Follow_Up message.

[0041] When the Transparent Clock 4 receives the Follow_Up message, it transmits the received Follow_Up message to the Client device. The Transparent Clock 4 sets the CF of the Follow_Up message to a value obtained by adding the transmission delay time pt1 between the Master device and the Transparent Clock 4 and the processing time of the Sync message in the Transparent Clock 4 (=pt1+(dt2-dt1)).

[0042] The client device calculates the reception time T2 of the Sync message at the client device using the following formula (4): T2 = T1 + pt1 + (dt2 - dt1) + pt2 Formula (4) based on the transmission time T1 of the Sync message by the master device, which is included in the Follow_Up message, the transmission delay time pt2 between the transparent clock 4 and the client device, the transmission delay time pt1 between the master device and the transparent clock 4, which is set in the CF of the Follow_Up message, and the processing time of the Sync message at the transparent clock 4.

[0043] The client device synchronizes its internal time with the calculated reception time T2 of the Sync message, thereby synchronizing the internal time of the client device with the internal time of the master device.

[0044] While the two-step method is described in FIG. 9 , the Follow_Up message and the Pdelay_Resp_Follow_Up message are not used in the one-step method. In this case, the transmission time T1 of the Sync message by the Master device, which was included in the Follow_Up message, can be included in the Sync message. The CF of the Sync message can be set to the sum (pt1+(dt2-dt1)) of the transmission delay time pt1 between the Master device and Transparent Clock 4 and the processing time of the Sync message in Transparent Clock 4 (dt2-dt1). The transmission time t3 of the Pdelay_Resp message by the Master device and the transmission time t7 of the Pdelay_Resp message by Transparent Clock 4, which were included in the Pdelay_Resp_Follow_Up message, can be set in the CF of the Pdelay_Resp message.

[0045] The E2E method described with reference to FIG. 8 and the P2P method described with reference to FIG. 9 mainly differ in the following two points.

[0046] The first difference is that the value of CF in the Follow_Up message is different. In the E2E method, the CF of the Follow_Up message sent from Transparent Clock 4 to the Client device is set to the processing time of the Sync message in Transparent Clock 4 (= dt2 - dt1). On the other hand, in the P2P method, the CF of the Follow_Up message sent from Transparent Clock 4 to the Client device is set to the sum of the transmission delay time pt1 between the Master device and Transparent Clock 4 and the processing time of the Sync message in Transparent Clock 4 (= pt1 + (dt2 - dt1)).

[0047] Therefore, in order for the Transparent Clock 4 to process both E2E and P2P messages, it is necessary to determine whether the message is an E2E Follow_Up message or a P2P Follow_Up message.

[0048] The second difference is that the types, transmission sections, and uses of the Req message and the Resp message are different.

[0049] The types of messages are Delay_Req and Delay_Resp messages in the E2E system, whereas they are Pdelay_Req, Pdelay_Resp, and Pdelay_Resp_Follow_Up messages in the P2P system.

[0050] In the E2E method, the message transmission section is between the Master device and the Client, whereas in the P2P method, it is between adjacent devices (between the Master device and Transparent Clock 4, and between Transparent Clock 4 and the Client device).

[0051] In the E2E method, the messages are used to measure and transmit values ​​necessary to calculate the offset between the Master device and the Client device (the sending and receiving times T3 and T4 of the Delay_Req message, and the processing time within the device of the Delay_Req message (dt4-dt3)), whereas in the P2P method, the messages are used to measure the transmission delay time between adjacent devices.

[0052] Therefore, in order for Transparent Clock 4 to process both E2E and P2P messages, the transmission section and usage must be changed depending on the type of message.

[0053] Due to the differences described above, devices using different profiles could not synchronize time with each other, and devices using the same profile had to be connected. Therefore, users of PTP had to build time distribution networks that used a single profile for each field, resulting in increased costs. Furthermore, network operators found it difficult to efficiently use their networks because a time distribution network used in one field could not generally distribute time to users in other fields. Therefore, there is a demand for technology that can distribute time to users in different fields (users using different profiles) over a single network.

[0054] As a configuration for realizing time synchronization using different profiles on a single network, for example, as shown in Fig. 10A, multiple Boundary Clocks 3 (in the example shown in Fig. 10A, three Boundary Clocks 3a, 3b, and 3c) are provided between Grand Master Clocks 1a and 1b that use different profiles and Client devices 2a and 2b that use different profiles, and the time is synchronized sequentially between adjacent devices. However, the Boundary Clock 3 can only synchronize time with one Grand Master Clock 1. Therefore, in the configuration shown in Fig. 10A, the Boundary Clock 3a cannot synchronize time with both the Grand Master Clocks 1a and 1b.

[0055] Another possible configuration for achieving time synchronization using different profiles on a single network is, for example, a configuration as shown in FIG. 10B in which multiple transparent clocks 4 (three transparent clocks 4a, 4b, and 4c in the example shown in FIG. 10B) are provided between grand master clocks 1a and 1b and client devices 2a and 2b. In this configuration, adjacent transparent clocks 4 are connected by a single line, and messages of multiple profiles are superimposed and transmitted between adjacent transparent clocks 4 on a single line. However, the transparent clock 4 cannot simultaneously process packets of different profiles on a single port corresponding to a single line. Therefore, in the configuration shown in FIG. 10B, packets of different profiles cannot be sequentially transferred between the grand master clock 1 and client device 2, and time synchronization using different profiles cannot be achieved on a single network.

[0056] Another possible configuration for achieving time synchronization using different profiles on a single network is, for example, a configuration as shown in FIG. 10C in which multiple transparent clocks 4 (three transparent clocks 4a, 4b, and 4c in the example shown in FIG. 10C ) are provided between grand master clocks 1a and 1b and client devices 2a and 2b. In this configuration, dedicated ports and lines are provided for each profile between adjacent transparent clocks 4. By setting the time correction method and PTP packet route for each port in advance, the grand master clock 1 and client device 2 can be time-synchronized for each of the multiple profiles. However, the configuration shown in FIG. 10C requires dedicated ports and lines for each profile, which increases the cost of building the system.

[0057] As described above, even when the conventional Boundary Clock 3 and Transparent Clock 4 are used, it is difficult to achieve time synchronization using different profiles on a single network.

[0058] The purpose of the present disclosure, made in consideration of the above-mentioned problems, is to provide a communication device, a communication system, and a communication method that can send and receive packets (PTP packets) of different profiles while suppressing increases in costs.

[0059] In order to solve the above problem, a communication device according to the present disclosure is a communication device that is connected to a first device that distributes time, and transmits and receives packets with another communication device that is connected to a second device that is time-synchronized with the time distributed from the first device, and includes a synchronization unit that synchronizes time with the other communication device, an acquisition unit that acquires control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device, a transmission delay time calculation unit that calculates a transmission delay time between the first device and the communication device, and a transmission delay time calculation unit that calculates the transmission delay time of the first packet transmitted by the first device, the ... The communication device includes a CF calculation unit that calculates a value of a correction field (CF), which is a correction value used for time correction in the second device, based on the transmission time of the packet, the calculated transmission delay time, and the reception time of the first packet by the communication device synchronized with the other communication device; a CF rewriting unit that rewrites the CF value included in the acquired control data with the calculated CF value; and a common format processing unit that transmits to the other communication device a packet in a format predetermined between the other communication device and the other communication device, which includes the control data after the CF value has been rewritten.

[0060] In addition, to solve the above problem, a communication device according to the present disclosure is a communication device that is connected to a second device that is time-synchronized with the time distributed from a first device, and that transmits and receives packets with other communication devices connected to the first device, and is equipped with a synchronization unit that synchronizes time with the other communication device, an acquisition unit that acquires control data that is contained in a packet of a predetermined format received from the other communication device and is data related to controlling the transmission and reception of a first packet transmitted from the first device to the other communication device, and a packet transmission / reception unit that transmits and receives packets with the second device, including a third packet according to the acquired control data, and the packet transmission / reception unit transmits to the second device a packet notifying the transmission and reception time of the packet between the communication device and the second device, synchronized with the first device, or the value of the CF, which is a correction value used for time correction in the second device and is contained in the control data, calculated based on the transmission time of the third packet, synchronized with the other communication device.

[0061] In order to solve the above-mentioned problem, a communication system according to the present disclosure is a communication system including a first device that distributes time, a second device that synchronizes with the time distributed from the first device, a first communication device connected to the first device, and a second communication device connected to the second device, wherein the first communication device and the second communication device are time-synchronized, and the first communication device acquires control data that is data related to control of transmission and reception of the first packet included in the first packet received from the first device, calculates a transmission delay time between the first device and the first communication device, and calculates a CF that is a correction value used for time correction in the second device based on the transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and the reception time of the first packet by the first communication device synchronized with the second communication device. and calculates a value of a CF (correctionField), rewrites the value of CF included in the acquired control data with the calculated CF value, and transmits a packet of a predetermined format between the second communication device and the second communication device, including the control data after the CF value has been rewritten, to the second communication device; the second communication device acquires the control data included in the packet of the predetermined format received from the first communication device, transmits and receives packets with the second device, including a third packet according to the acquired control data, and transmits to the second device a packet notifying the transmission and reception time of the packet between the second communication device and the second device, synchronized with the first device, or the value of the CF, calculated based on the value of the CF (correctionField) included in the control data and the transmission time of the third packet, synchronized with the first communication device.

[0062] In order to solve the above-mentioned problem, a communication method according to the present disclosure is a communication method in a communication system including a first device that distributes time, a second device that synchronizes with the time distributed from the first device, a first communication device connected to the first device, and a second communication device connected to the second device, wherein the first communication device and the second communication device are time-synchronized, and the first communication device acquires control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device, calculates a transmission delay time between the first device and the first communication device, and calculates a correction value used for time correction in the second device based on a transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and a reception time of the first packet by the first communication device synchronized with the second communication device. the second communication device acquires the control data contained in the packet of the predetermined format received from the first communication device, transmits a packet to the second communication device, the packet including a third packet according to the acquired control data, and transmits a packet to the second communication device notifying the transmission / reception time of the packet between the second communication device and the second communication device, synchronized with the first device, or the value of the CF, which is calculated based on the value of the CF (correction Field) contained in the control data and the transmission time of the third packet, synchronized with the first communication device.

[0063] According to the communication device, communication system, and communication method disclosed herein, packets of different profiles can be transmitted and received while suppressing increases in costs.

[0064] 7B is a diagram illustrating an example configuration of a communication system according to the present disclosure. FIG. 7B is a diagram illustrating an overview of the operation of the communication system illustrated in FIG. 1. FIG. 7C is a diagram illustrating time synchronization using the E2E method in the communication system illustrated in FIG. 1. FIG. 7D is a diagram illustrating time synchronization using the P2P method in the communication system illustrated in FIG. 1. FIG. 7E is a diagram illustrating an example configuration of a communication device illustrated in FIG. 1. FIG. 7F is a diagram illustrating an example hardware configuration of the communication device illustrated in FIG. 7C is a diagram illustrating an example configuration of a time synchronization system. FIG. 7G is a diagram illustrating another example configuration of a time synchronization system. FIG. 7H is a diagram illustrating time synchronization using the E2E method in the time synchronization system illustrated in FIG. 7B is a diagram illustrating time synchronization using the P2P method in the time synchronization system illustrated in FIG. 7H is a diagram illustrating an example network configuration assumed for time synchronization using different profiles. FIG. 7H is a diagram illustrating another example network configuration assumed for time synchronization using different profiles. FIG. 7H is a diagram illustrating a further example network configuration assumed for time synchronization using different profiles.

[0065] Hereinafter, embodiments of the present disclosure will be described with reference to the drawings.

[0066] FIG. 1 is a diagram illustrating an example configuration of a communication system 10 according to an embodiment of the present disclosure.

[0067] As shown in FIG. 1, a communication system 10 according to this embodiment includes Grand Master Clocks 1a and 1b, communication devices 100a and 100b, a Transparent Clock 4, and client devices 2a and 2b.

[0068] The Grand Master Clocks 1a and 1b, which serve as first devices, are devices that have a master function for distributing their own internal time. The Grand Master Clocks 1a and 1b use different profiles for time synchronization.

[0069] The client devices 2a and 2b, which are second devices, are devices equipped with slave functions. The client devices 2a and 2b use different profiles for time synchronization. For example, the Grand Master Clock 1a and the client device 2a use the same profile for time synchronization. The Grand Master Clock 1b and the client device 2b also use the same profile for time synchronization.

[0070] The transparent clock 4 transfers packets between the communication device 100a and the communication device 100b.

[0071] The communication device 100a as a first communication device is connected to the Grand Master Clocks 1a and 1b, and transmits and receives packets (PTP packets) to and from the Grand Master Clocks 1a and 1b according to the profiles used by each device. The communication device 100b as a second communication device is connected to the Client devices 2a and 2b, and transmits and receives packets (PTP packets) to and from the Client devices 2a and 2b according to the profiles used by each device.

[0072] Furthermore, the communication devices 100a and 100b are each connected to a transparent clock 4 and transmit and receive packets via the transparent clock 4. Packets in a common, predetermined format (common format) are transmitted and received between the communication devices 100a and 100b regardless of the profile. As described above, the transparent clock 4 cannot simultaneously process packets of different profiles on a single port. In this embodiment, packets in a common format are transmitted and received between the communication devices 100a and 100b. Therefore, by connecting the communication device 100a and the transparent clock 4 and the communication device 100b and the transparent clock 4 with a single line, packets can be transmitted and received between the communication devices 100a and 100b. Therefore, as shown in FIG. 10C , there is no need to provide ports and lines for each profile. Furthermore, a conventional transparent clock 4 can be used as is in the communication system 10 according to this embodiment. This eliminates the need to add ports and lines or modify existing devices, thereby suppressing cost increases.

[0073] Furthermore, in the communication system 10 according to this embodiment, the communication devices 100a and 100b are time-synchronized (phase-synchronized) by transmitting and receiving packets via the Transparent Clock 4. Phase synchronization refers to synchronization between the internal clocks of the communication devices 100a and 100b, and does not necessarily mean synchronization with TAI or UTC (Universal Time Coordinated).

[0074] Next, the operation of each device in the communication system 10 according to this embodiment will be described. Fig. 2 is a diagram showing an overview of the operation of each device in the communication system 10 according to this embodiment, and is a diagram for explaining a communication method by the communication system 10 according to this embodiment.

[0075] As described above, the communication device 100a and the communication device 100b are time-synchronized (phase-synchronized). First, the operation for time synchronization between the communication device 100a and the communication device 100b will be described.

[0076] The communication device 100a transmits a Sync message and a Follow_Up message to the communication device 100b via Transparent Clock 4.

[0077] When the communication device 100b receives the Sync message and the Follow_Up message transmitted from the communication device 100a, it transmits a Delay_Req message to the communication device 100a.

[0078] When the communication device 100a receives the Delay_Req message transmitted from the communication device 100b, it transmits a Delay_Resp message to the communication device 100b.

[0079] By exchanging messages in this manner, the communication device 100a and the communication device 100b can be time-synchronized (phase-synchronized) by the same process as in FIG.

[0080] Next, the operation for synchronizing the time between the Grand Master Clock 1 and the client device 2 will be described.

[0081] The Grand Master Clock 1 transmits a Sync message and a Follow_Up message as a first packet to the communication device 100a. The Grand Master Clock 1 includes the transmission time T1 of the Sync message in the Follow_Up message.

[0082] The communication device 100a receives the Sync message and Follow_Up message transmitted from the Grand Master Clock 1. The communication device 100a acquires control data contained in the received Sync message and Follow_Up message, which is data related to controlling the transmission and reception of these packets. The communication device 100a acquires, for example, header information and TLV (Type Length Value) information contained in the Sync message and Follow_Up message as the control data. The TLV information is optional information for PTP.

[0083] The communication device 100a calculates the transmission delay time pt1 between the Grand Master Clock 1 and the communication device 100a. Specifically, the communication device 100a calculates the transmission delay time pt1 between the Grand Master Clock 1 and the communication device 100a by transmitting and receiving messages (Req messages and Resp messages) to and from the Grand Master Clock 1 according to the profile used by the Grand Master Clock 1.

[0084] The communication device 100a calculates the value of CF based on the transmission time T1 of the Sync message by Grand Master Clock 1, the calculated transmission delay time pt1, and the reception time dt1 of the Sync message by the communication device 100a synchronized with the communication device 100b. As described above, the transmission time T1 of the Sync message by Grand Master Clock 1 is included in the Follow_Up message and notified to the communication device 100a.

[0085] The communication device 100a rewrites the CF value included in the acquired control data with the calculated CF value, and transmits to the communication device 100b packets (Sync' message and Follow_Up' message) in a format that is predetermined for communication with the communication device 100b and that includes the control data after the rewritten CF value.

[0086] The communication device 100b receives the Sync' message and Follow_Up' message transmitted from the communication device 100a, and acquires the control data included in the received Sync' message or Follow_Up' message.

[0087] The communication device 100b transmits a Sync message and a Follow_Up message as third packets according to the acquired control data to the client device 2. That is, the communication device 100b transmits the Sync message and the Follow_Up message, which have header information and TLV information according to the control data, to the client device 2.

[0088] The communication device 100b transmits to the client device 2 a packet notifying the transmission / reception time of a packet between the communication device 100b and the client device 2, which is synchronized with the Grand Master Clock 1 and calculated based on the CF value included in the acquired control data and the transmission time dt4 of the Sync message synchronized with the communication device 100a, or the CF value. As will be described in detail later, the client device 2 can synchronize with the grand master clock 1 using the transmission / reception time or the CF value transmitted from the communication device 100b.

[0089] As described with reference to FIG. 2, in the communication method by the communication system 10 according to this embodiment, the communication device 100a (first communication device) and the communication device 100b (second communication device) are time-synchronized.

[0090] The communication device 100a acquires control data included in the Sync message and Follow_Up message (first packet) received from Grand Master Clock 1 (first device). The communication device 100a calculates a transmission delay time pt1 between Grand Master Clock 1 and the communication device 100a. The communication device 100a calculates a CF value based on the transmission time T1 of the Sync message by Grand Master Clock 1 notified by Grand Master Clock 1, the calculated transmission delay time pt1, and the reception time dt1 of the Sync message by the communication device 100a synchronized with the communication device 100b. The communication device 100a rewrites the CF value included in the acquired control data with the calculated CF value. The communication device 100a transmits a packet in a format predetermined for communication with the communication device 100b to the communication device 100b, including the control data after the CF value has been rewritten.

[0091] The communication device 100b acquires control data contained in a packet of a predetermined format received from the communication device 100a. The communication device 100b transmits and receives packets to and from the client device 2, including a Sync message and a Follow_Up message (third packet) corresponding to the acquired control data. The communication device 100b transmits to the client device 2 a packet notifying the transmission and reception time of the packet between the communication device 100b and the client device 2, synchronized with the Grand Master Clock 1, or the CF value, calculated based on the CF value contained in the control data and the Sync message transmission time dt4 synchronized with the communication device 100a.

[0092] In the communication system 10 according to this embodiment, the communication devices 100a and 100b are time-synchronized (phase-synchronized), and therefore the processing time of a PTP packet in the relay device (communication devices 100a and 100b and Transparent Clock 4) can be calculated as the difference (= dt4 - dt1) between the transmission time dt4 of the Sync message by communication device 100b and the reception time dt1 of the Sync message by communication device 100a. Therefore, the calculation method of the processing time of a PTP packet in the relay device can be unified regardless of the profile used.

[0093] Furthermore, in the communication system 10 according to this embodiment, the communication device 100a connected to the Grand Master Clock 1 does not need to synchronize time with the Grand Master Clock 1. Therefore, the communication device 100a can process messages from multiple Grand Master Clocks 1a and 1b that use different profiles.

[0094] Furthermore, in the communication system 10 according to this embodiment, packets in a predetermined format are transmitted and received between the communication device 100a and the communication device 100b. Therefore, if the communication device 100a and the communication device 100b are connected via a single line, packets can be transmitted and received between the communication device 100a and the communication device 100b regardless of the profile. Therefore, there is no need to provide a port and line for each profile or to modify the Transparent Clock 4.

[0095] Therefore, according to the communication system 10 according to the present disclosure, packets (PTP packets) of different profiles can be transmitted and received while suppressing increases in costs.

[0096] Next, the operation of the communication system 10 according to this embodiment will be described in more detail. In the following description, the profiles are assumed to be an E2E profile and a P2P profile, which use different methods for measuring transmission delay. First, the operation when time synchronization is performed between the Grand Master Clock 1 and the Client device 2 using the E2E profile will be described with reference to FIG. 3. Note that the packet transmission times and reception times of each device will be appropriately denoted as times T1, T2, ..., times t1, t2, ..., and times dt1, dt2, ..., but the numbers included in each symbol are not necessarily assigned in chronological order.

[0097] First, the operation of time synchronization between the communication device 100a and the communication device 100b will be described.

[0098] At time T4, communication device 100a transmits a Sync message to Transparent Clock 4. Upon receiving the Sync message transmitted from communication device 100a at time dt5, Transparent Clock 4 transmits a Sync message to communication device 100b at time dt6.

[0099] After transmitting the Sync message, communication device 100a transmits a Follow_Up message to Transparent Clock 4. Communication device 100a includes the transmission time T4 of the Sync message in the Follow_Up message. Upon receiving the Follow_Up message transmitted from communication device 100a, Transparent Clock 4 transmits the Follow_Up message to communication device 100b. Transparent Clock 4 sets the processing time D1 (= dt6 - dt5) of the Sync message at Transparent Clock 4 in CF of the Follow_Up message.

[0100] At time T5, the communication device 100b receives the Sync message transmitted from the Transparent Clock 4. The communication device 100b also receives the Follow_Up message transmitted from the Transparent Clock 4.

[0101] At time T6, communication device 100b transmits a Delay_Req message to Transparent Clock 4. Upon receiving the Delay_Req message transmitted from communication device 100b at time dt7, Transparent Clock 4 transmits a Delay_Req message to communication device 100a at time dt8.

[0102] At time T7, communication device 100a receives the Delay_Req message transmitted from Transparent Clock 4. Upon receiving the Delay_Req message, communication device 100a transmits a Delay_Resp message to Transparent Clock 4. Communication device 100b includes the reception time T7 of the Delay_Req message in the Delay_Resp message.

[0103] When Transparent Clock 4 receives the Delay_Resp message transmitted from communication device 100a, it transmits the Delay_Resp message to communication device 100b. Transparent Clock 4 sets the processing time D2 (=dt8-dt7) of the Delay_Req message in Transparent Clock 4 in the CF of the Delay_Resp message.

[0104] Communication device 100b receives the Delay_Resp message transmitted from Transparent Clock 4. Communication device 100b calculates an offset, which is the difference between the device time of communication device 100a and the device time of communication device 100b, based on the time T4 when communication device 100a transmitted the Sync message, the time T5 when communication device 100b received the Sync message, the time T6 when communication device 100b transmitted the Delay_Req message, the time T7 when communication device 100a received the Delay_Req message, the processing time D1 of the Sync message on Transparent Clock 4, and the processing time D2 of the Delay_Req message on Transparent Clock 4, and synchronizes the device time of communication device 100b with the device time of communication device 100a.

[0105] Next, the time synchronization between the Grand Master Clock 1 and the client device 2 will be described.

[0106] At time T1, Grand Master Clock 1 transmits a Sync message to communication device 100a. After transmitting the Sync message, Grand Master Clock 1 transmits a Follow_Up message to communication device 100a. Grand Master Clock 1 includes the transmission time T1 of the Sync message in the Follow_Up message. In this way, the transmission time T1 of the Sync message by Grand Master Clock 1 is notified to communication device 100a.

[0107] The communication device 100a receives the Sync message and the Follow_Up message transmitted from the Grand Master Clock 1. The communication device 100a stores the reception time dt1 of the Sync message. The communication device 100a terminates the received Sync message and Follow_Up message at the communication device 100a without transparently forwarding them.

[0108] If the CF of the received Follow_Up message is 0, the Follow_Up message is a message from Grand Master Clock 1, not a message from a relay device in the network. In this case, communication device 100a transmits to Grand Master Clock 1 a Delay_Req message, which is an E2E Req message, and a Pdelay_Req message, which is a P2P Req message. Both the Delay_Req message and the Pdelay_Req message are transmitted because communication device 100a does not know whether Grand Master Clock 1 uses an E2E profile or a P2P profile. Note that only the Delay_Req message is illustrated in FIG. 3. Communication device 100a stores the transmission time t1 of the Req message.

[0109] The Grand Master Clock 1 receives the Req message transmitted from the communication device 100a and stores the reception time t2 of the Req message. The Grand Master Clock 1 then transmits a Resp message to the communication device 100a. In the example shown in FIG. 3, the Grand Master Clock 1 uses an E2E profile. Therefore, when the Grand Master Clock 1 receives the Delay_Req message from the communication device 100a, it stores the reception time t2. The Grand Master Clock 1 then transmits a Delay_Resp message to the communication device 100a. The Grand Master Clock 1 includes the reception time t2 of the Delay_Req message in the Delay_Resp message.

[0110] The communication device 100a receives the Delay_Resp message transmitted from the Grand Master Clock 1. Because the Delay_Resp message, which is a message used in the E2E system, has been transmitted from the Grand Master Clock 1, the communication device 100a stores the E2E system profile as the profile used by the Grand Master Clock 1.

[0111] The communication device 100a calculates the transmission delay time pt1 between the Grand Master Clock 1 and the communication device 100a using the following equation (5) based on the time dt1 when the communication device 100a receives the Sync message, the time T1 when the Grand Master Clock 1 transmits the Sync message contained in the Follow_Up message, the time t1 when the communication device 100a transmits the Delay_Req message, and the time t2 when the Grand Master Clock 1 receives the Delay_Resp message. pt1=((dt1-T1)+(t2-t1)) / 2 Equation (5)

[0112] The communication device 100a acquires and stores, as control data, header information and TLV (Type Length Value) information contained in the received Sync message and Follow_Up message. The header information includes domainNumber and sourcePortIdentity. The domainNumber indicates the group of devices performing time synchronization. The sourcePortIdentity indicates the sender of the message. By storing this information, it is possible to identify and store the device that sent the Sync message or Follow_Up message.

[0113] The communication device 100a calculates the value of CF based on the transmission time T1 of the Sync message by Grand Master Clock 1 notified from Grand Master Clock 1 (contained in the Follow_Up message), the calculated transmission delay time pt1, and the reception time dt1 of the Sync message by communication device 100a synchronized with communication device 100b. Specifically, the communication device 100a calculates the value of CF using the following equation (6): CF=T1+pt1-dt1 (Equation (6))

[0114] The communication device 100a rewrites the CF value included in the acquired control data with the calculated CF value.

[0115] At time dt2, communication device 100a transmits a Sync' message in a common format predetermined between communication device 100b and communication device 100b to communication device 100b. Communication device 100a also transmits a Follow_Up' message in a common format to communication device 100b. Communication device 100a includes control data after the CF value has been rewritten in the Sync' message or Follow_Up' message. FIG. 3 shows an example in which the CF value calculated using equation (6) is included in the Sync' message. When communication device 100a is connected to multiple Grand Master Clocks 1 as shown in FIG. 1, communication device 100a includes control data obtained from the Sync message and Follow_Up message of each Grand Master Clock 1 in the Sync' message or Follow_Up' message.

[0116] The Transparent Clock 4 transparently transfers the Sync' message and Follow_Up' message in the common format transmitted from the communication device 100a to the communication device 100b. If the Transparent Clock 4 recognizes the Sync' message and Follow_Up' message as normal PTP packets, the CF value will be rewritten. Therefore, the packets in the common format must be encapsulated or otherwise processed so that they are not recognized as PTP packets.

[0117] Communication device 100b receives the Sync' message and Follow_Up' message transmitted from communication device 100a via Transparent Clock 4. Communication device 100a stores the reception time dt3 of the Sync' message. Communication device 100a terminates the received Sync' message and Follow_Up' message at communication device 100b without transparently forwarding them.

[0118] The communication device 100b acquires the control data included in the Sync' message or Follow_Up' message. The communication device 100b transmits a Sync message and a Follow_Up message corresponding to the acquired control data to the client device 2. Here, the communication device 100b acquires and stores the domainNumber included in the Delay_Req message received from the client device 2. That is, the communication device 100b stores the groups with which the multiple client devices 2 connected to the communication device 100b are time-synchronized. The client device 2 periodically transmits a Delay_Req message. The communication device 100b can use this Delay_Req message to determine the groups with which the multiple client devices 2 are time-synchronized. The communication device 100b transmits the Sync message and the Follow_Up message from the port that received the Delay_Req message containing the domainNumber that matches the domainNumber of the Sync message and the Follow_Up message.

[0119] The communication device 100b stores the transmission time dt4 of the Sync message. As described above, the communication devices 100a and 100b are time-synchronized. Therefore, the transmission time dt4 of the Sync message is synchronized with the communication device 100a. The communication device 100b calculates the transmission time T1' of the Sync message, synchronized with Grand Master Clock 1, using the following equation (7) based on the CF value (= T1 + pt1 - dt1) included in the acquired control data and the transmission time dt4 of the Sync message. T1' = T1 + pt1 + (dt4 - dt1) Equation (7)

[0120] The communication device 100b includes the calculated transmission time T1' of the Sync message in the Follow_Up message.

[0121] At time T2, the client device 2 receives the Sync message sent from the communication device 100b, and also receives the Follow_Up message sent from the communication device 100b.

[0122] At time T3, the client device 2 transmits a Delay_Req message to the communication device 100b.

[0123] When the communication device 100b receives the Delay_Req message transmitted from the client device 2 at time t4, it transmits a Delay_Resp message to the client device 2. As described above, the communication devices 100a and 100b are time-synchronized (phase-synchronized). Therefore, the reception time t4 of the Delay_Req message is synchronized with the communication device 100a. The communication device 100b calculates the reception time T4' of the Delay_Req message synchronized with the Grand Master Clock 1, based on the CF value (= T1 + pt1 - dt1) included in the acquired control data and the reception time t4 of the Delay_Req message, using the following equation (8): T4' = T1 + pt1 + (t4 - dt1) Equation (8)

[0124] The communication device 100b includes the calculated reception time T4' of the Delay_Req message in the Delay_Resp message.

[0125] Client device 2 receives the Delay_Resp message sent from communication device 100b. Based on the time T1' of the Sync message sent by communication device 100b synchronized with Grand Master Clock 1, which are included in the Follow_Up message, the time T2 of the Sync message sent by communication device 100b, the time T3 of the Delay_Req message sent by client device 2, and the time T4' of the Delay_Resp message received by communication device 100b synchronized with Grand Master Clock 1, client device 2 calculates the offset between Grand Master Clock 1 and client device 2 using the following equation (9): Offset = ((T2 - T1') - (T4' - T3)) / 2 Equation (9)

[0126] The client device 2 synchronizes its own internal time with the internal time of the Grand Master Clock 1 based on the calculated offset.

[0127] Next, the operation of synchronizing time between the Grand Master Clock 1 using a P2P profile and the Client device 2 will be described with reference to Fig. 4. Note that the operation for synchronizing time between the communication device 100a and the communication device 100b is the same as in the E2E method, and therefore the description thereof will be omitted.

[0128] At time T1, Grand Master Clock 1 transmits a Sync message to communication device 100a. After transmitting the Sync message, Grand Master Clock 1 transmits a Follow_Up message to communication device 100a. Grand Master Clock 1 includes the transmission time T1 of the Sync message in the Sync message. In this way, the transmission time T1 of the Sync message by Grand Master Clock 1 is notified to communication device 100a.

[0129] The communication device 100a receives the Sync message and the Follow_Up message transmitted from the Grand Master Clock 1. The communication device 100a stores the reception time dt1 of the Sync message. The communication device 100a terminates the received Sync message and Follow_Up message at the communication device 100a without transparently forwarding them.

[0130] If the CF of the received Follow_Up message is 0, the Follow_Up message is a message from Grand Master Clock 1, not a message from a relay device in the network. In this case, the communication device 100a transmits a Delay_Req message and a Pdelay_Req message to Grand Master Clock 1. The reason for transmitting both the Delay_Req message and the Pdelay_Req message is that the communication device 100a does not know whether Grand Master Clock 1 uses an E2E profile or a P2P profile. Note that only the Pdelay_Req message is shown in FIG. 4. The communication device 100a stores the transmission time t1 of the Req message.

[0131] The Grand Master Clock 1 receives the Req message transmitted from the communication device 100a and stores the time t2 at which the Req message was received. Then, at time t3, the Grand Master Clock 1 transmits a Resp message to the communication device 100a. In the example shown in FIG. 4 , the Grand Master Clock 1 uses a P2P profile. Therefore, when the Grand Master Clock 1 receives the Pdelay_Req message from the communication device 100a, it stores the time t2 at which the Pdelay_Req message was received. Then, the Grand Master Clock 1 transmits a Pdelay_Resp message to the communication device 100a. The Grand Master Clock 1 includes the time t2 at which the Pdelay_Req message was received in the Pdelay_Resp message.

[0132] After transmitting the Pdelay_Resp message, the Grand Master Clock 1 transmits a Pdelay_Resp_Follow_up message to the communication device 100a. The Grand Master Clock 1 includes the transmission time t3 of the Pdelay_Resp message in the Pdelay_Resp_Follow_up message.

[0133] At time t4, communication device 100a receives the Pdelay_Resp message transmitted from Grand Master Clock 1. Because the Pdelay_Resp message, which is a message used in the P2P system, has been transmitted from Grand Master Clock 1, communication device 100a stores the P2P system profile as the profile to be used by Grand Master Clock 1.

[0134] The communication device 100a calculates the transmission delay time pt1 between the Grand Master Clock 1 and the communication device 100a using the following equation (10) based on the time dt1 when the communication device 100a receives the Sync message, the time T1 when the Grand Master Clock 1 transmits the Sync message, which is included in the Follow_Up message, the time t1 when the communication device 100a transmits the Pdelay_Req message, and the time t2 when the Grand Master Clock 1 receives the Pdelay_Resp message. pt1=((dt1-T1)+(t2-t1)) / 2 Equation (10)

[0135] The communication device 100a acquires and stores, as control data, header information, TLV information, and the like, contained in the received Sync message and Follow_Up message. The header information includes domain number and source port identity. By storing this information, the device that sent the Sync message and Follow_Up message can be identified and stored.

[0136] The communication device 100a calculates the value of CF based on the transmission time T1 of the Sync message by Grand Master Clock 1 notified from Grand Master Clock 1 (contained in the Follow_Up message), the calculated transmission delay time pt1, and the reception time dt1 of the Sync message by communication device 100a, which is synchronized with communication device 100b. Specifically, the communication device 100a calculates the value of CF using the following equation (11): CF=T1+pt1-dt1 (Equation (11))

[0137] The communication device 100a rewrites the CF value included in the acquired control data with the calculated CF value.

[0138] At time dt2, communication device 100a transmits a Sync' message in a common format predetermined between communication device 100b and communication device 100b to communication device 100b. Communication device 100a also transmits a Follow_Up' message in a common format to communication device 100b. Communication device 100a includes control data after the CF value has been rewritten in the Sync' message or Follow_Up' message. FIG. 4 shows an example in which the CF value calculated using equation (11) is included in the Sync' message. When communication device 100a is connected to multiple Grand Master Clocks 1 as shown in FIG. 1, communication device 100a includes control data obtained from the Sync message and Follow_Up message of each Grand Master Clock 1 in the Sync' message or Follow_Up' message.

[0139] The Transparent Clock 4 transparently transfers the Sync' message and Follow_Up' message in the common format transmitted from the communication device 100a to the communication device 100b.

[0140] Communication device 100b receives the Sync' message and Follow_Up' message transmitted from communication device 100a via Transparent Clock 4. Communication device 100a stores the reception time dt3 of the Sync' message. Communication device 100a terminates the received Sync' message and Follow_Up' message at communication device 100b without transparently forwarding them.

[0141] The communication device 100b acquires the control data included in the Sync' message or Follow_Up' message. The communication device 100b transmits a Sync message and a Follow_Up message corresponding to the acquired control data to the client device 2. The communication device 100b then acquires and stores the domain number included in the Pdelay_Req message received from the client device 2. That is, the communication device 100b stores the groups with which the multiple client devices 2 connected to the communication device 100b are time-synchronized. The client device 2 periodically transmits a Pdelay_Req message. The communication device 100b can use this Pdelay_Req message to determine the groups with which the multiple client devices 2 are time-synchronized. The communication device 100b transmits the Sync message and the Follow_Up message from the port that received the Pdelay_Req message, which includes a domain number that matches the domain number of the Sync message and the Follow_Up message.

[0142] The communication device 100b stores the transmission time dt4 of the Sync message. As described above, the communication device 100a and the communication device 100b are time-synchronized (phase-synchronized). Therefore, the transmission time dt4 of the Sync message is synchronized with the time of the communication device 100a. The communication device 100b calculates the value of CF using the following equation (12) based on the value of CF (= T1 + pt1 - dt1) included in the acquired control data and the transmission time dt4 of the Sync message. CF = T1 + pt1 + dt4 - dt1 Equation (12)

[0143] The communication device 100b sets the calculated CF value to the CF of the Follow_Up message.

[0144] At time T2, the client device 2 receives the Sync message sent from the communication device 100b, and also receives the Follow_Up message sent from the communication device 100b.

[0145] At time t5, the client device 2 transmits a Pdelay_Req message to the communication device 100b.

[0146] When the communication device 100b receives the Pdelay_Req message transmitted from the client device 2 at time t6, the communication device 100b transmits a Pdelay_Resp message to the client device 2 at time t7. The communication device 100b includes the reception time t6 of the Pdelay_Req message in the Pdelay_Resp message.

[0147] After transmitting the Pdelay_Resp message, the communication device 100b transmits a Pdelay_Resp_Follow_up message to the client device 2. The communication device 100b includes a transmission time t7 of the Pdelay_Resp message in the Pdelay_Resp_Follow_up message.

[0148] At time t8, the client device 2 receives the Pdelay_Resp message transmitted from the communication device 100b, and also receives the Pdelay_Resp_Follow_up message transmitted from the communication device 100b.

[0149] The client device 2 calculates the transmission delay time pt2 between the communication device 100b and the client device 2 using the following equation (13) based on the time t5 when the client device 2 sends the Pdelay_Req message, the time t6 when the communication device 100b receives the Pdelay_Req message included in the Pdelay_Resp message, the time t7 when the communication device 100b sends the Pdelay_Resp message included in the Pdelay_Resp_Follow_up message, and the time t8 when the client device 2 receives the Pdelay_Resp message: pt2=((t6-t5)+(t8-t6)) / 2 Equation (13)

[0150] Based on the calculated transmission delay time pt2, the client device 2 calculates the reception time T2 of the Sync message synchronized with the Grand Master Clock 1 using the following equation (14), and synchronizes the internal time of the client device 2 with the internal time of the Grand Master Clock 1. T2=T1+pt1+dt4-dt1+pt2 (Equation (14))

[0151] 3 and 4, in this embodiment, the communication device 100a and the communication device 100b are time-synchronized, and packets are transmitted and received in a common format between the communication device 100a and the communication device 100b. In this way, the Grand Master Clock 1 and the client device 2 can be time-synchronized whether an E2E profile or a P2P profile is used.

[0152] Next, the configurations of the communication devices 100a and 100b will be described. In the following, when there is no need to distinguish between the communication devices 100a and 100b, they will be referred to as the communication device 100.

[0153] Fig. 5 is a diagram showing an example of the configuration of a communication device 100 according to this embodiment. In Fig. 5, it is assumed that the profile used by the Grand Master Clock 1 and the client device 2 is an E2E profile or a P2P profile.

[0154] As shown in FIG. 5 , the communication device 100 according to this embodiment includes packet transmitting / receiving units 101 and 102, an E2E / P2P determination unit 103, an E2E / P2P registration unit 104, an E2E processing unit 105, a P2P processing unit 106, a transmission delay time calculation unit 107, an acquisition unit 108, a CF calculation unit 109, a CF rewriting unit 110, an assignment unit 111, a common format processing unit 112, a time correction unit 113, a destination designation unit 114, an internal clock 115, and a phase synchronization unit 116.

[0155] The packet transmitting / receiving unit 101 transmits and receives packets (PTP packets) to and from the Grand Master Clock 1 or the client device 2. In the communication device 100a, the packet transmitting / receiving unit 101 transmits and receives packets to and from the Grand Master Clock 1. In the communication device 100b, the packet transmitting / receiving unit 101 transmits and receives packets to and from the client device 2.

[0156] In the communication device 100b, the packet transmitter / receiver 101 transmits and receives packets to and from the client device 2, including a Sync message (third packet) corresponding to the control data acquired by the communication device 100. As described with reference to Fig. 3, in the E2E system, the packet transmitter / receiver 101 transmits to the client device 2 packets (Follow_Up message and Delay_Resp message) notifying the transmission and reception times of packets between the communication device 100b and the client device 2 (transmission time T1' of the Sync message and reception time T4' of the Delay_Req message) synchronized with the Grand Master Clock 1, which are calculated based on the CF value included in the control data and the transmission time dt4 of the Sync message synchronized with the communication device 100a (another communication device). 4, in the P2P system, the packet transmitter / receiver 101 transmits a packet (Follow_Up message) notifying the client device 2 of the CF value (=T1+pt1+dt4-dt1) calculated based on the CF value included in the control data and the transmission time dt4 of the Sync message synchronized with the communication device 100a (another communication device). The packet transmitter / receiver 101 transmits a packet notifying the transmission / reception time of the packet or the CF value to the client device 2 in accordance with the profile determined by the E2E / P2P determination unit 103 (described later).

[0157] Depending on the received packet, the packet transmitter / receiver 101 outputs the packet received from the Grand Master Clock 1 or the client device 2 to the E2E / P2P determination unit 103, the E2E processing unit 105, the P2P processing unit 106, the transmission delay time calculation unit 107, the acquisition unit 108, the CF calculation unit 109, or the destination instruction unit 114. Furthermore, the packet transmitter / receiver 101 transmits the packets output from the E2E processing unit 105 and the P2P processing unit 105 in accordance with instructions from the destination instruction unit 114, which will be described later.

[0158] The packet transmitter / receiver 102 transmits and receives packets to and from the Transparent Clock 4. The packet transmitter / receiver 102 outputs the packet received from the Transparent Clock 4 to the acquisition unit 108, the destination designation unit 114, or the phase synchronization unit 116, depending on the received packet.

[0159] Based on a packet output from the packet transmitter / receiver 101, the E2E / P2P determination unit 103 determines whether the Grand Master Clock 1 or the client device 2 that transmitted the packet uses an E2E profile or a P2P profile. For example, when the E2E / P2P determination unit 103 receives a Delay_Req message or a Delay_Resp message, it determines that the sender of the message uses an E2E profile. Furthermore, for example, when the E2E / P2P determination unit 103 receives a Pdelay_Req message or a Pdelay_Resp message, it determines that the sender of the message uses a P2P profile. The header information of the Req message and the Resp message includes a messageType that indicates the type of the message. The E2E / P2P determination unit 103 can determine the type of the received message based on the value of messageType.

[0160] In this way, the E2E / P2P determination unit 103 as a profile determination unit determines a profile to be used by the Grand Master Clock 1 from among multiple profiles (E2E / P2P) with different transmission delay measurement methods, based on information (messageType) indicating the packet type included in the Delay_Resp message / Pdelay_Resp message (second packet) received from the Grand Master Clock 1. Also, the E2E / P2P determination unit 103 determines a profile to be used by the Client device 2 from among multiple profiles (E2E / P2P) with different transmission delay measurement methods, based on information (messageType) indicating the packet type included in the Delay_Req message / Pdelay_Req received from the Client device 2.

[0161] The E2E / P2P registration unit 104 stores the determination result of the E2E / P2P determination unit 103 on the profiles used by the Grand Master Clock 1 and the client device 2 .

[0162] The E2E processing unit 105 processes the packets transmitted and received by the packet transmitting and receiving unit 101 as E2E packets according to the determination result of the E2E / P2P determining unit 103 .

[0163] The P2P processing unit 106 processes the packets transmitted and received by the packet transmitting and receiving unit 101 as P2P packets according to the determination result of the E2E / P2P determining unit 103 .

[0164] When the communication device 100 is the communication device 100a, the transmission delay time calculation unit 107 calculates the transmission delay time pt1 between the Grand Master Clock 1 and the communication device 100. The transmission delay time calculation unit 107 calculates the transmission delay time pt1 by transmitting and receiving packets to and from the Grand Master Clock 1 according to the profile determined by the E2E / P2P determination unit 103. Specifically, when the Grand Master Clock 1 uses an E2E profile, the transmission delay time calculation unit 107 calculates the transmission delay time pt1 by transmitting and receiving Delay_Req messages and Delay_Resp messages, as described with reference to FIG. 3. Furthermore, when the Grand Master Clock 1 uses a P2P profile, the transmission delay time calculation unit 107 calculates the transmission delay time pt1 by transmitting and receiving Pdelay_Req messages and Pdelay_Resp messages, as described with reference to FIG. 4.

[0165] In the communication device 100a, the acquisition unit 108 acquires control data, which is data related to the transmission and reception of a Sync message and a Follow_Up message (first packet) received from Grand Master Clock 1 (first device). The acquisition unit 108 acquires, for example, header information and TLV information of the Sync message and the Follow_Up message as control data. The acquisition unit 108 also stores the domain number and source port identity included in the control data. In the communication device 100b, the acquisition unit 108 acquires control data included in the Sync' message or the Follow_Up' message received from the communication device 100a via Transparent Clock 4.

[0166] The CF calculation unit 109 calculates the value of CF, which is a correction value used for time correction in the client device 2. In the communication device 100a, the CF calculation unit 109 calculates the value of CF (= T1 + pt1 - dt1) based on the transmission time T1 of the Sync message by Grand Master Clock 1 notified from Grand Master Clock 1, the transmission delay time pt1 calculated by the transmission delay time calculation unit 107, and the reception time dt1 of the Sync message by communication device 100a synchronized with communication device 100b. In the case of the P2P method, in the communication device 100b, the CF calculation unit 109 calculates the value of CF (= T1 + pt1 + dt4 - dt1) based on the value of CF included in the control data acquired by the acquisition unit 108 and the transmission time dt4 of the Sync message by communication device 100b.

[0167] The CF rewriting unit 110 rewrites the CF value included in the control data acquired by the acquisition unit 108 with the CF value calculated by the CF calculation unit 109 .

[0168] When the communication device 100 is the communication device 100a, the adding unit 111 adds the control data acquired by the acquiring unit 108 to a Sync' message or a Follow_Up' message in a common format transmitted by the packet transmitting / receiving unit 102. In addition, the adding unit 111 outputs the control data acquired by the acquiring unit 108 to the common format processing unit 112.

[0169] The common format processing unit 112 processes the transmission and reception of messages in a common format between the communication device 100a and the communication device 100b. When the control data output from the adding unit 111 is output (i.e., when the communication device 100 receives a Sync message and a Follow_Up message from the Grand Master Clock 1), the common format processing unit 112 causes the packet transmitting / receiving unit 102 to transmit a Sync' message and a Follow_Up' message. As described above, the Sync' message or Follow_Up' message in the common format includes the acquired control data. Furthermore, the CF value included in the control data is rewritten to the CF value calculated by the CF calculation unit 109. Therefore, when the communication device 100 is the communication device 100a, the common format processing unit 112 transmits to the communication device 100b a packet in a format predetermined between the communication device 100a and the communication device 100b, which includes the control data after the CF value has been rewritten.

[0170] When the communication device 100 is the communication device 100b, the time correction unit 113 corrects the time to be notified to the client device 2 to a time synchronized with the internal device time of the Grand Master Clock 1. Specifically, as described with reference to FIG. 4, the time correction unit 113 corrects the transmission time dt4 of the Sync message by the communication device 100b to the transmission time T1' of the Sync message synchronized with the Grand Master Clock 1. The time correction unit 113 also corrects the reception time t4 of the Delay_Req message by the communication device 100b to the reception time T4' of the Delay_Req message synchronized with the Grand Master Clock 1. As described above, the transmission time T1' of the Sync message is notified to the client device 2 by a Follow_Up message. The reception time T4' of the Delay_Req message is notified to the client device 2 by a Delay_Resp message.

[0171] The destination instruction unit 114 refers to the domainNumber and sourcePortIdentity stored in the acquisition unit 108 and instructs the packet transmission / reception units 101 and 102 on the destination of each message.

[0172] The phase synchronization unit 116 synchronizes (phase synchronizes) the internal clock 115, which is the internal time of the communication device 100, with the internal time of other communication devices by transmitting and receiving packets between the communication device 100a and the communication device 100b as described with reference to Figures 3 and 4.

[0173] 5 has been described as an example in which the communication device 100a and the communication device 100b have the same configuration, but the present disclosure is not limited to this. The communication device 100a only needs to have the configuration necessary for the operation of the communication device 100a among the configurations of the communication device 100 shown in FIG. 5. Furthermore, the communication device 100b only needs to have the configuration necessary for the operation of the communication device 100b among the configurations of the communication device 100 shown in FIG. 5.

[0174] As described above, the communication system 10 according to this embodiment includes a Grand Master Clock 1 (first device) that distributes time, a Client device 2 (second device) that synchronizes with the time distributed from the Grand Master Clock 1, a communication device 100a (first communication device) connected to the Grand Master Clock 1, and a communication device 100b (second communication device) connected to the Client device 2. The communication devices 100a and 100b are time-synchronized (phase-synchronized).

[0175] The communication device 100a acquires control data relating to the control of transmission and reception of the first packet, which is included in the first packet (Sync message and Follow_Up message) received from Grand Master Clock 1. The communication device 100a calculates a transmission delay time pt1 between Grand Master Clock 1 and the communication device 100a. The communication device 100a calculates a CF value, which is a correction value used for time correction in the client device 2, based on the transmission time of the first packet by Grand Master Clock 1 notified by Grand Master Clock 1, the calculated transmission delay time pt1, and the reception time of the first packet by communication device 100a, which is synchronized with communication device 100b. The communication device 100a rewrites the CF value included in the acquired control data with the calculated CF value. The communication device 100a transmits to the communication device 100b packets (Sync' message and Follow_Up' message) in a format predetermined between the communication device 100b and the communication device 100b, the packets including the control data after the CF value has been rewritten.

[0176] The communication device 100b acquires control data contained in a packet of a predetermined format received from the communication device 100a. The communication device 100b transmits and receives packets to and from the client device 2, including a third packet (a Sync' message and a Follow_Up' message) corresponding to the acquired control data. The communication device 100b transmits to the client device 2 a packet notifying the transmission and reception time of the packet between the communication device 100b and the client device 2, synchronized with the Grand Master Clock 1, or the CF value, calculated based on the CF value contained in the acquired control data and the transmission time of the third packet, synchronized with the communication device 100a.

[0177] By time-synchronizing (phase-synchronizing) the communication devices 100a and 100b, the processing time of a PTP packet in a relay device between the Grand Master Clock 1 and the Client device 2 can be calculated as the difference (=dt4-dt1) between the time dt4 when the Sync message was sent by the communication device 100b and the time dt1 when the Sync message was received by the communication device 100a. Therefore, the calculation method of the processing time of a PTP packet in a relay device can be unified regardless of the profile used.

[0178] Furthermore, the communication device 100a connected to the Grand Master Clock 1 does not need to synchronize time with the Grand Master Clock 1. Therefore, the communication device 100a can process messages from multiple Grand Master Clocks 1a and 1b that use different profiles.

[0179] Furthermore, by transmitting and receiving packets in a predetermined format between the communication devices 100a and 100b, if the communication devices 100a and 100b are connected by a single line, packets can be transmitted and received between the communication devices 100a and 100b regardless of the profile. Therefore, there is no need to provide ports and lines for each profile or to modify Transparent Clock 4.

[0180] Therefore, according to the communication system 10 according to the present disclosure, packets (PTP packets) of different profiles can be transmitted and received while suppressing increases in costs.

[0181] Next, the hardware configuration of the communication device 100 according to the present disclosure will be described.

[0182] 6 is a diagram illustrating an example of a hardware configuration of a communication device 100 according to the present disclosure. In FIG. 6, an example of the hardware configuration of the communication device 100 is illustrated, in which the communication device 100 is configured by a computer capable of executing program instructions. Here, the computer may be a general-purpose computer, a dedicated computer, a workstation, a personal computer (PC), an electronic notepad, or the like. The program instructions may be program code, code segments, or the like for performing necessary tasks.

[0183] 6, the communication device 100 includes a processor 201, a read-only memory (ROM) 202, a random access memory (RAM) 203, a storage 204, an input unit 205, a display unit 206, and a communication interface (I / F) 207. Each component is communicably connected to one another via a bus 209. The processor 201 is specifically 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 by multiple processors of the same type or different types.

[0184] The processor 201 is a control unit that controls each component and performs various arithmetic processing. That is, the processor 201 reads a program from the ROM 202 or the storage 204 and executes the program using the RAM 203 as a work area. The processor 201 controls each component and performs various arithmetic processing in accordance with the program stored in the ROM 202 or the storage 204. In this embodiment, the ROM 202 or the storage 204 stores a program for operating a computer as the communication device 100 according to the present disclosure. The program is read and executed by the processor 201, thereby realizing each component of the communication device 100 described above.

[0185] The program may be provided in a form stored on a non-transitory storage medium such as a CD-ROM (Compact Disk Read Only Memory), a DVD-ROM (Digital Versatile Disk Read Only Memory), a USB (Universal Serial Bus) memory, etc. The program may also be provided in a form downloaded from an external device via a network.

[0186] The ROM 202 stores various programs and various data. The RAM 203 temporarily stores programs or data as a working area. The storage 204 is configured with an HDD (Hard Disk Drive) or an SSD (Solid State Drive) and stores various programs including the operating system and various data.

[0187] The input unit 205 includes a pointing device such as a mouse and a keyboard, and is used to input various types of information.

[0188] The display unit 206 is, for example, a liquid crystal display, and displays various information. The display unit 206 may be a touch panel type and function as the input unit 205.

[0189] The communication interface 207 is an interface for communicating with other devices (for example, the Grand Master Clock 1, the Client device 2, and the Transparent Clock 4).

[0190] A computer can be suitably used to function as each unit of the above-described communication device 100. Such a computer can be realized by storing a program describing the processing content for realizing the functions of each unit of the communication device 100 in a memory unit of the computer, and having the processor of the computer read and execute the program. In other words, the program can cause the computer to function as the above-described communication device 100. The program can also be recorded on a non-transitory storage medium. The program can also be provided via a network.

[0191] The following additional notes are provided regarding the above-described embodiments.

[0192] [Supplementary Item 1] A communication device connected to a first device that distributes time, and configured to transmit and receive packets with another communication device connected to a second device that is time-synchronized with the time distributed from the first device, comprising: a control unit, wherein the control unit is configured to: time-synchronize with the other communication device; acquire control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device; calculate a transmission delay time between the first device and the communication device; calculate a value of a correction field (CF) that is a correction value used for time correction in the second device, based on the transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and the reception time of the first packet by the communication device synchronized with the other communication device; rewrite the value of the correction field included in the acquired control data with the calculated CF value; and transmit to the other communication device a packet in a format predetermined between the other communication device and the communication device, the packet including the control data after the CF value has been rewritten.

[0193] [Supplementary Item 2] In the communication device described in Supplementary Item 1, the control unit determines a profile to be used by the first device from a plurality of profiles with different transmission delay measurement methods based on information indicating a type of the second packet received from the first device, and calculates the transmission delay time by transmitting and receiving packets to and from the first device according to the determined profile.

[0194] [Supplementary Item 3] A communication device connected to a second device that is time-synchronized with a time distributed from a first device, and that transmits and receives packets with another communication device connected to the first device, comprising a control unit, wherein the control unit is configured to: time-synchronize with the other communication device; acquire control data that is contained in a packet of a predetermined format received from the other communication device and is data related to controlling the transmission and reception of a first packet transmitted from the first device to the other communication device; transmit and receive packets with the second device that include a third packet according to the acquired control data; and transmit to the second device a packet notifying the transmission and reception time of the packet between the communication device and the second device synchronized with the first device, or the value of the CF, which is contained in the control data and is a correction value used for time correction in the second device, and which is calculated based on the transmission time of the third packet synchronized with the other communication device.

[0195] [Supplementary Item 4] In the communication device described in Supplementary Item 3, the control unit determines a profile to be used by the second device from a plurality of profiles having different methods of measuring transmission delay, based on information indicating a type of the packet contained in the packet received from the second device, and transmits a packet to the second communication device notifying the transmission / reception time of the packet or the value of the CF according to the determined profile.

[0196] [Supplementary Item 5] A communication system comprising a first device that distributes time, a second device that synchronizes with the time distributed from the first device, a first communication device connected to the first device, and a second communication device connected to the second device, wherein the first communication device and the second communication device are time-synchronized, the first communication device acquires control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device, calculates a transmission delay time between the first device and the first communication device, calculates a value of a correction field (CF) that is a correction value used for time correction in the second device based on the transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and the reception time of the first packet by the first communication device synchronized with the second communication device, rewrites the value of CF included in the acquired control data with the calculated value of CF, A communication system comprising: a first communication device and a second communication device; a second communication device; a second communication device; a first communication device; a second communication device; a second communication device; a first communication device; a second communication device; a second communication device; a first communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a second communication device; a first ...

[0197] [Supplementary Item 6] A communication method in a communication system including a first device that distributes time, a second device that synchronizes with the time distributed from the first device, a first communication device connected to the first device, and a second communication device connected to the second device, wherein the first communication device and the second communication device are time-synchronized, and the first communication device: acquires control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device; calculates a transmission delay time between the first device and the first communication device; calculates a value of a correction field (CF) that is a correction value used for time correction in the second device based on the transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and the reception time of the first packet by the first communication device synchronized with the second communication device; rewrites the value of CF included in the acquired control data with the calculated value of CF; A communication method comprising: transmitting a packet of a predetermined format between the second communication device and the second communication device, the packet including control data after the CF value has been rewritten; the second communication device: acquiring the control data included in the packet of the predetermined format received from the first communication device; transmitting and receiving packets with the second device, the packet including a third packet according to the acquired control data; and transmitting to the second device a packet notifying the transmission and reception time of the packet between the second communication device and the second device, synchronized with the first device, or the value of the CF, calculated based on the value of the CF (correction field) included in the control data and the transmission time of the third packet, synchronized with the first communication device.

[0198] Although the above-described embodiments have been described as typical examples, it will be apparent to those skilled in the art that many modifications and substitutions can be made within the spirit and scope of the present disclosure. Therefore, the present invention should not be interpreted as being limited by the above-described embodiments, and various modifications and alterations are possible without departing from the scope of the claims. For example, multiple building blocks shown in the block diagrams of the embodiments can be combined into one, or one building block can be divided.

[0199] DESCRIPTION OF SYMBOLS 1, 1a, 1b Grand Master Clock (first device) 2, 2a, 2b Client device (second device) 3, 3a, 3b, 3c Boundary Clock 4, 4a, 4b, 4c Transparent Clock 10 Communication system 100, 100a, 100b Communication device 101, 102 Packet transmitting / receiving unit 103 E2E / P2P determination unit (profile determination unit) 104 E2E / P2P registration unit 105 E2E processing unit 106 P2P processing unit 107 Transmission delay time calculation unit 108 Acquisition unit 109 CF calculation unit 110 CF rewriting unit 111 Assignment unit 112 Common format processing unit 113 Time correction unit 114 Destination designation unit 115 Internal clock 116 Phase synchronization unit 201 Processor 202 ROM 203 RAM 204 Storage 205 Input unit 206 Display unit 207 Communication I / F 209 Bus

Claims

1. A communication device connected to a first device that distributes time and that transmits and receives packets with another communication device connected to a second device that is time-synchronized with the time distributed from the first device, comprising: a synchronization unit that synchronizes time with the other communication device; an acquisition unit that acquires control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device; a transmission delay time calculation unit that calculates a transmission delay time between the first device and the communication device; a CF calculation unit that calculates a value of a correction field (CF), which is a correction value used for time correction in the second device, based on the transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and the reception time of the first packet by the communication device synchronized with the other communication device; and a CF rewrite unit that rewrites the value of CF included in the acquired control data to the calculated CF value. a common format processing unit that transmits to the other communication device a packet in a format predetermined between the other communication device and the other communication device, the packet including the control data after the CF value has been rewritten.

2. A communication device connected to a second device that performs time synchronization with a time distributed from a first device, and that transmits and receives packets with another communication device connected to the first device, comprising: a synchronization unit that performs time synchronization with the other communication device; an acquisition unit that acquires control data contained in a packet of a predetermined format received from the other communication device, the control data being data related to control of transmission and reception of a first packet transmitted from the first device to the other communication device; and a packet transmission / reception unit that transmits and receives packets with the second device, the packet transmission / reception unit including a third packet according to the acquired control data, wherein the packet transmission / reception unit transmits to the second device a packet notifying the transmission / reception time of the packet between the communication device and the second device synchronized with the first device, or the value of the CF, calculated based on a value of a correction field (CF) contained in the control data, which is a correction value used for time correction in the second device, and the transmission time of the third packet synchronized with the other communication device.

3. A communication system comprising a first device that distributes time, a second device that synchronizes with the time distributed from the first device, a first communication device connected to the first device, and a second communication device connected to the second device, wherein the first communication device and the second communication device are time-synchronized, the first communication device acquires control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device, calculates a transmission delay time between the first device and the first communication device, calculates a value of a correction field (CF) that is a correction value used for time correction in the second device based on the transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and the reception time of the first packet by the first communication device synchronized with the second communication device, and rewrites the value of CF included in the acquired control data to the calculated CF value, a packet in a predetermined format between the second communication device and the second communication device, the packet including control data after the CF value has been rewritten; the second communication device acquires the control data included in the packet in the predetermined format received from the first communication device, transmits and receives packets with the second device, the packet including a third packet corresponding to the acquired control data, and transmits to the second device a packet notifying the second device of the transmission and reception time of the packet between the second communication device and the second device, synchronized with the first device, or the value of the CF, calculated based on the value of the CF (correction Field) included in the control data and the transmission time of the third packet, synchronized with the first communication device.

4. A communication method in a communication system including a first device that distributes time, a second device that synchronizes with the time distributed from the first device, a first communication device connected to the first device, and a second communication device connected to the second device, wherein the first communication device and the second communication device are time-synchronized, and the first communication device: acquires control data that is data related to control of transmission and reception of the first packet included in a first packet received from the first device; calculates a transmission delay time between the first device and the first communication device; calculates a value of a correction field (CF), which is a correction value used for time correction in the second device, based on the transmission time of the first packet by the first device notified from the first device, the calculated transmission delay time, and the reception time of the first packet by the first communication device synchronized with the second communication device; rewrites the value of CF included in the acquired control data to the calculated CF value; A communication method comprising: transmitting a packet of a predetermined format between the second communication device and the second communication device, the packet including control data after the CF value has been rewritten; the second communication device acquiring the control data included in the packet of the predetermined format received from the first communication device; transmitting and receiving packets with the second device, the packet including a third packet corresponding to the acquired control data; and transmitting to the second device a packet notifying the transmission and reception time of the packet between the second communication device and the second device, synchronized with the first device, or the value of the CF, calculated based on the value of the CF (correction Field) included in the control data and the transmission time of the third packet, synchronized with the first communication device.

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