Communication system, communication device and communication method
A communication system according to one aspect of the present disclosure is a communication system in which a plurality of communication devices are connected to a network. The plurality of communication devices include a time master including a master clock that manages time of the communication system and a plurality of time slaves each of which includes a slave clock time-synchronized with the master clock. Each of the plurality of time slaves includes a synchronization unit that performs time synchronization with another communication device connected adjacent to a master side on the network and a communication unit that notifies the time master of time synchronization information indicating time synchronization accuracy of the own device obtained by the synchronization unit.
1. A communication system in which a plurality of communication devices are connected to a network,
wherein
the plurality of communication devices includes:
a time master including a master clock that manages time of the communication system; and
a plurality of time slaves each of which includes a slave clock that is time-synchronized with the master clock,
each time slave of the plurality of time slaves includes:
a synchronization module that performs time synchronization with a first communication device connected adjacent to the each time slave at a master side on the network; and
a communication module that notifies the time master of time synchronization information indicating time synchronization accuracy of the each time slave obtained by the synchronization module,
the synchronization module corrects time of the each time slave by using a difference between time of the first communication device and the time of the each time slave as a time adjustment value, and
the communication module notifies the time master of the time adjustment value as the time synchronization information.
2. The communication system according to claim 1 , wherein
the communication module
receives the time adjustment value from a second communication device that is connected adjacent to the each time slave at a slave side on the network, and
transfers either one of the received time adjustment value or the time adjustment value of the each time slave to the first communication device, the transferred time adjustment value having a greater one in absolute values of the received time adjustment value and the time adjustment value of the each time slave.
3. The communication system according to claim 2 , wherein
the synchronization module periodically performs time synchronization processing of correcting the time of the each time slave by exchanging a time synchronization packet with the first communication device, and
the communication module stores the time adjustment value to be transferred to the first communication device in the time synchronization packet to be transmitted to the first communication device.
4. The communication system according to claim 1 , wherein
the communication module
receives the time adjustment value from a second communication device connected adjacent to the each time slave at a slave side on the network, and
transfers the received time adjustment value and the time adjustment value of the each time slave to the first communication device.
5. The communication system according to claim 1 , wherein
the communication module
receives the time adjustment value from a second communication device connected adjacent to the each time slave at a slave side on the network, and
transfers a sum of the received time adjustment value and the time adjustment value of the each time slave to the first communication device.
6. The communication system according to claim 1 , wherein
the time master is a control device that manages data transmission in the network,
the each time slave is a device that performs the data transmission according to an instruction from the control device, and
the control device
determines whether the time synchronization with the plurality of devices is completed based on the time synchronization information of which the plurality of devices notify the control device, and
starts the data transmission in the network when the time synchronization is determined to be completed.
7. The communication system according to claim 1 , wherein
one of the plurality of time slaves is a control device that manages data transmission in the network,
remaining time slaves of the plurality of time slaves and the time master are each a device that performs the data transmission according to an instruction from the control device,
the time master
determines whether the time synchronization with the plurality of time slaves is completed based on the time synchronization information of which the plurality of time slaves notify the time master, and
notifies the control device of a determination result, and
the control device starts the data transmission in the network when the time synchronization is determined to be completed from the determination result.
8. The communication system according to claim 1 , wherein
one of the plurality of time slaves is a control device that manages data transmission in the network,
remaining time slaves of the plurality of time slaves and the time master are each a device that performs the data transmission according to an instruction from the control device,
the time master transfers the time synchronization information of which the plurality of time slaves notify the time master to the control device, and
the control device
determines whether the time synchronization with the plurality of devices is completed based on the time synchronization information, and
starts the data transmission in the network when the time synchronization is determined to be completed.
9. The communication system according to claim 1 , wherein
the synchronization module periodically performs time synchronization processing of correcting the time of the each time slave by exchanging a time synchronization packet with the first communication device, and
the communication module notifies the time master of the time synchronization information after the performance of the time synchronization processing.
10. A communication device network-connected to a communication system including a time master that includes a master clock that manages time of the communication system,
the communication device comprising:
a slave clock that is time-synchronized with the master clock;
a synchronization module that performs time synchronization with a first communication device connected adjacent to the communication device at a master side on the network; and
a communication module that notifies the time master of time synchronization information that indicates time synchronization accuracy of the communication device obtained by the synchronization module,
wherein
the synchronization module corrects time of the communication device by using a difference between time of the first communication device and the time of the communication device as a time adjustment value, and
the communication module notifies the time master of the time adjustment value as the time synchronization information.
11. A communication method in a communication system in which a plurality of communication devices are connected to a network, the plurality of communication devices including:
a time master including a master clock that manages time of the communication system; and
a plurality of time slaves each of which includes a slave clock that is time-synchronized with the master clock,
the communication method comprising:
time-synchronizing each time slave of the plurality of time slaves with a first communication device connected adjacent to the each time slave at a master side on the network; and
notifying the time master of time synchronization information that indicates time synchronization accuracy of the each time slave,
wherein
the time-synchronizing includes correcting time of the each time slave by using a difference between time of the first communication device and the time of the each time slave as a time adjustment value, and
the notifying the time master includes notifying the time master of the time adjustment value of the each time slave as the time synchronization information.