A communication system and a communication method for one-way transmission are provided. The communication method includes: receiving, by a router, a first synchronization message from a grandmaster clock; generating, by the router, a timestamp according to the first synchronization message; receiving, by the router, at least one data packet; transmitting, by the router, the at least one data packet and the timestamp to a programmable logic device; and outputting, by the programmable logic device, the at least one data packet and the timestamp.

A distributed network system can include a master controller having a master clock configured to output a master time, and a master transmission delay time module configured to modify the master time to add a known master transmission delay to the master time to output an adjusted master time. The system can include a first device operatively connected to the master controller and configured to receive the adjusted master time from the master controller.

In some embodiments, a method is performed after locking a first clock of a computing device to synchronize with a second clock associated with a first device where a difference between the first clock and the second clock is determined during the locking. The method measures a path delay to a second device based on sending messages including first timestamps of the first clock to the second device and receiving messages including second timestamps of a third clock from the second device. A third message is sent to the second device that includes a third timestamp of the first clock that has been locked to the second clock, wherein the third message includes the path delay, and wherein the third timestamp and the path delay allow the second device to analyze a lock quality of the first clock to the second clock based on a time of the third clock.

A time-synchronization system according to the present disclosure includes a relay apparatus (10) configured to perform time-synchronization with a master apparatus (30) through a transmission system of which a transmission delay changes depending on a transmission direction, and a relay apparatus (20) configured to perform time-synchronization with the relay apparatus (10), in which the relay apparatus (20) transmits information about a difference between first time information obtained by performing time-synchronization with the relay apparatus (10) and second time information obtained from a time-synchronization source to the relay apparatus (10), and the relay apparatus (10) corrects third time information obtained by performing time-synchronization with the master apparatus (30) by using the information about the difference, and performs time-synchronization with a slave apparatus (50) by using the corrected third time information.

A time providing method includes: by a computer, upon receiving data from a device, estimating a generation time of the data using a reception time of the data and a first delay time of the device previously estimated; providing information indicating the generation time to the data; and transmitting the data provided with the information indicating the generation time to a destination of the data.

A time synchronization method includes receiving, by a receive-end device, a first timestamp and a first header signal sent by a transmit-end device, where the first timestamp indicates a first moment at which a first channel medium conversion module sends the first header signal, and a second moment at which the receive-end device receives the first header signal. The method further includes sending a second header signal to the transmit-end device, where a third moment at which the receive-end device sends the second header signal. The method further includes receiving a fourth timestamp sent by the transmit-end device, where the fourth timestamp indicates a fourth moment at which the transmit-end device receives the second header signal. The method further includes synchronizing time with the transmit-end device based on the first moment, the second moment, the third moment, and the fourth moment.

A physical layer (PHY) processor of a network device receives a timing message via an external network and generates a first timestamp using a first local-domain clock used by the PHY processor. The PHY processor transfers the timing message and the first timestamp to a packet processor of the network device via an internal communication link. The packet processor generates a second timestamp for the timing message using a domain-specific clock. The packet processor determines a delay value using the first timestamp, the delay value accounting for a time delay corresponding to the transfer of the timing message within the network device from the PHY processor to the packet processor. The packet processor adjusts the second timestamp using the delay value to generate an adjusted domain-specific timestamp for the timing message.

In order to synchronize the respective local network time of participants of a real-time network, wherein the participants are connected to one another via ports, the participants transmit, preferably cyclically, synchronization packets to connected participants, wherein one participant of the real-time network is designated as the synchronization master, and using the synchronization packets, the local network time of the other participants is synchronized with the local network time of the synchronization master.

A packet processing method includes receiving a first packet by a first receiving interface of a media conversion module of a first network device, where the first packet includes a first alignment marker (AM), sending a second packet by a first sending interface of the media conversion module, where the second packet includes the first AM, and where the second packet is the first packet processed by the media conversion module, and calculating a time interval T.sub.1 between a time at which the media conversion module receives the first packet and a time at which the media conversion module sends the second packet, where the T.sub.1 is used to compensate for a first timestamp at which the first network device receives or sends the third packet.

A method for communications is proposed. The method may comprise receiving, by a first network node, a report of clock quality of a second network node from a third network node. A clock of the first network node is selected as a master clock for synchronization in a first timing domain, a clock of the second network node is selected as a is selected as a master clock for synchronization in a second timing domain, and the third network node is attached to at least the first timing domain and the second timing domain. Based at least in part on the received report, it may be determined whether to synchronize the first timing domain to the second timing domain. In response to the determination of synchronizing the first timing domain to the second timing domain, the first network node can obtain timing information of the second network node from the third network node. The method may further comprise tuning the clock of the first network node to synchronize the first timing domain to the second timing domain, based at least in part on the timing information of the second network node.