Network devices and associated methods are provided for synchronization in an optically switched network. The network device includes one or more ports in communication with a plurality of devices via an optical switch. The one or more ports receive a master clock signal having a first frequency from a first device of the plurality of devices. The network device includes a local clock in communication with the one or more ports and operating at a second frequency. The network device includes a synchronization manager in communication with the one or more ports and the local clock and configured to be enabled and disabled. When the synchronization manager is enabled, it receives the master clock signal via the one or more ports and transmits an instruction to the local clock to operate at the first frequency.

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.

A network system for a data center is described in which a switch fabric provides interconnectivity such that any servers may communicate packet data to any other of the servers using any of a number of parallel data paths. Moreover, according to the techniques described herein, edge-positioned access nodes, permutation devices and core switches of the switch fabric may be configured and arranged in a way such that the parallel data paths provide single L2/L3 hop, full mesh interconnections between any pairwise combination of the access nodes, even in massive data centers having tens of thousands of servers. The access nodes may be arranged within access node groups, and permutation devices may be used within the access node groups to spray packets across the access node groups prior to injection within the switch fabric, thereby increasing the fanout and scalability of the network system.

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.

A network switching system and method and a computer program product for operating a network switch are disclosed. The network switch includes a multitude of input ports and a multitude of output ports. In one embodiment, one processing device is assigned to each of the input ports and output ports to process data packets received at the input ports and transferred to the output ports. In one embodiment, the method comprises creating an intermediate adjustable configuration of processing devices functionally between the input ports and the output ports, and assigning the processing devices of the intermediate configuration to forward the data packets from the input ports to the output ports to obtain a balance between latency and synchronization of the transfer of the data packets from the input ports to the output ports. In an embodiment, software is used to create and to adjust dynamically the intermediate configuration.

A network system for a data center is described in which a switch fabric provides full mesh interconnectivity such that any servers may communicate packet data to any other of the servers using any of a number of parallel data paths. Moreover, according to the techniques described herein, edge-positioned access nodes, permutation devices and core switches of the switch fabric may be configured and arranged in a way such that the parallel data paths provide single L2/L3 hop, full mesh interconnections between any pairwise combination of the access nodes, even in massive data centers having tens of thousands of servers. The access nodes may be arranged within access node groups, and permutation devices may be used within the access node groups to spray packets across the access node groups prior to injection within the switch fabric, thereby increasing the fanout and scalability of the network system.

A network switching system and method and a computer program product for operating a network switch are disclosed. The network switch includes a multitude of input ports and a multitude of output ports. In one embodiment, one processing device is assigned to each of the input ports and output ports to process data packets received at the input ports and transferred to the output ports. In one embodiment, the method comprises creating an intermediate adjustable configuration of processing devices functionally between the input ports and the output ports, and assigning the processing devices of the intermediate configuration to forward the data packets from the input ports to the output ports to obtain a balance between latency and synchronization of the transfer of the data packets from the input ports to the output ports. In an embodiment, software is used to create and to adjust dynamically the intermediate configuration.

Methods and stations for transmission delay measurements are disclosed. The method includes controlling, by a first station, an optical path selector to work in a first state, and selecting, by the first station, a first fiber to send a first OSC signal to a second station, where the first OSC signal includes a first time stamp. The method further includes controlling, by the first station, the optical path selector to work in a second state, and selecting, by the first station, the first fiber to receive a second OSC signal from the second station at a second receiving moment, where the second OSC signal includes a second time stamp. The method further includes calculating, by the first station, a unidirectional transmission delay between the first station and the second station based on a first sending moment, a first receiving moment, a second sending moment, and the second receiving moment.

Embodiments of the present invention disclose a method for switching a modulation format of a passive optical network, an apparatus, and a system. The method includes: separately delivering, by an OLT, a registration message to an optical network unit in all supported upstream modulation formats and/or downstream modulation formats; receiving, by the OLT, a first message reported by the optical network unit, where the first message includes an upstream modulation format capability and/or a downstream modulation format capability; and determining, by the OLT, a target upstream modulation format and/or a target downstream modulation format of the optical network unit according to the first message, and instructing the optical network unit to switch to the target upstream modulation format and/or the target downstream modulation format. Therefore, in a PON system that supports a plurality of modulation formats, a modulation format reporting capability of the ONU is improved.

Systems and methods for performing impairment compensation in point-to-multi-point communication systems are described. In a data snapshot mode, a hub node can send instructions to each communication node connected to the hub node to send a data snapshot of data being received and processed by the communication nodes at a particular time. In a trench line mode, a hub node sends instructions to each communication node to send trench line data back to the hub node. The hub node uses the data snapshot or trench line data to determine how to tune filter coefficients in the hub node to perform impairment compensation and improve performance of the communication system.