Embodiments of the present disclosure relate to methods, optical line terminals (OLTs), optical network units (ONUs), apparatuses and computer storage media for transmitting a time synchronization message. In some example embodiments, the OLT is configured to: determine a threshold rate to be N messages per second for transmission of a time synchronization message to an ONU, wherein N being greater than or equal to 0.1; and transmit, to the ONU, a time synchronization message at the threshold rate or a rate above the threshold rate, to enable the ONU to perform time synchronization with the OLT. In some other example embodiments, the OLT is configured to: select a plurality of ONUs for transmitting time synchronization information; and transmit, to the ONUs, a broadcast or multicast message the time synchronization information, to enable the plurality of ONUs to perform time synchronization with the OLT.

A method for securing the time synchronization of an Ethernet on-board network of a motor vehicle, by: determining a delay time of a first signal on a first connecting path between a first control unit of the network and a second control unit of the network; determining a maximum speed of the first connecting path on the basis of the delay time; and determining a type of a transmission medium of the first connecting path on the basis of the maximum speed. The determination of the delay time of a first signal, the determination of the maximum speed of the first connecting path, and the determination of the type of a transmission medium of the first connecting path result in an entropy source being formed that is used to ascertain at least one dynamic key for the connecting path to encrypt a time synchronization message for the connecting path.

This technology allows time synchronization in passive optical networks (“PON”). A first Ethernet device timestamps and transmits a packet to a second Ethernet device via the PON. The first Ethernet device transmits the packet to a small form-factor pluggable (“SFP”) device within the PON and connected to the first Ethernet device. The SFP device determines a transmission time to a second SFP device and modifies a correction field (“CF”) of the packet by subtracting an ingress time and the transmission time from the CF. The packet is transmitted to the second SFP device, which modifies the CF by the addition of an egress time. The modified CF value represents the real-time transmission delay incurred in the SFP devices. The packet is transmitted to a second Ethernet device to synchronize a clock using the timestamp and the CF value in accordance with the PTP/IEEE-1588 standard.

Embodiments including methods, systems, and apparatuses for distributing, processing, and reacting to path information distributed via a service-agnostic packet fabric for the purpose of enabling path selection are disclosed. By configuring two ingress line cards to send path quality words to each other via the switch fabric, compare the path quality words, and determine whether to transmit traffic to an egress line card via the switch fabric based on the comparison of the path quality words, the embodiments enable a central switch fabric to be unaware of the paths that it carries, and enable both ingress and egress bandwidth of the switch fabric to be sized according to the facilities for which it is terminating. The switch fabric does not need to support working and protection paths simultaneously in some embodiments, allowing it to be scaled appropriately to termination facilities.

This application provides a communication method and an optical module. The method includes: A first optical module determines a first delay. The first optical module sends the first delay to an interface chip. According to the communication method and the optical module that are provided in this application, a delay in the optical module can be reported to the interface chip, so as to improve precision of time synchronization between a master clock and a slave clock, thereby further improving clock precision of a network device.

This technology allows time synchronization in passive optical networks (“PON”). A first Ethernet device timestamps and transmits a packet to a second Ethernet device via the PON. The first Ethernet device transmits the packet to a small form-factor pluggable (“SFP”) device within the PON and connected to the first Ethernet device. The SFP device determines a transmission time to a second SFP device and modifies a correction field (“CF”) of the packet by subtracting an ingress time and the transmission time from the CF. The packet is transmitted to the second SFP device, which modifies the CF by the addition of an egress time. The modified CF value represents the real-time transmission delay incurred in the SFP devices. The packet is transmitted to a second Ethernet device to synchronize a clock using the timestamp and the CF value in accordance with the PTP/IEEE-1588 standard.

Embodiments of the present disclosure relate to methods, optical line terminals (OLTs), optical network units (ONUs), apparatuses and computer storage media for transmitting a time synchronization message. In some example embodiments, the OLT is configured to: determine a threshold rate to be N messages per second for transmission of a time synchronization message to an ONU, wherein N being greater than or equal to 0.1; and transmit, to the ONU, a time synchronization message at the threshold rate or a rate above the threshold rate, to enable the ONU to perform time synchronization with the OLT. In some other example embodiments, the OLT is configured to: select a plurality of ONUs for transmitting time synchronization information; and transmit, to the ONUs, a broadcast or multicast message comprising the time synchronization information, to enable the plurality of ONUs to perform time synchronization with the OLT.

In an aspect, an apparatus for distribution of frequency reference to a receiving end over a transmission medium comprises a first mixer adapted to mix a frequency reference signal having a reference frequency with a local oscillator signal having a local oscillator frequency to provide a forward frequency reference signal, a communication section adapted to transmit the forward frequency reference signal and receive a first backward frequency reference signal, a second mixer adapted to mix the first backward frequency reference signal with the local oscillator signal to provide a second backward frequency reference signal and a phase comparator and control circuit adapted to adjust the local oscillator frequency based on a phase shift of the second backward frequency reference signal so as to compensate for a phase shift of the forward frequency reference signal.

In an aspect, an apparatus for distribution of frequency reference to a receiving end over a transmission medium comprises a first mixer adapted to mix a frequency reference signal having a reference frequency with a local oscillator signal having a local oscillator frequency to provide a forward frequency reference signal, a communication section adapted to transmit the forward frequency reference signal and receive a first backward frequency reference signal, a second mixer adapted to mix the first backward frequency reference signal with the local oscillator signal to provide a second backward frequency reference signal and a phase comparator and control circuit adapted to adjust the local oscillator frequency based on a phase shift of the second backward frequency reference signal so as to compensate for a phase shift of the forward frequency reference signal.

This application provides a communication method and an optical module. The method includes: A first optical module determines a first delay. The first optical module sends the first delay to an interface chip. According to the communication method and the optical module that are provided in this application, a delay in the optical module can be reported to the interface chip, so as to improve precision of time synchronization between a master clock and a slave clock, thereby further improving clock precision of a network device.