Method and devices for synchronization

摘要

This invention relates to methods and devices for time and frequency synchronization. The invention has particular application where time and frequency synchronization over packet networks using, for example, the IEEE 1588 Precision Time Protocol (PTP) is being carried out. The primary challenge in clock distribution over packet networks is the variable transit delays experienced by timing packets, packet delay variations (PDVs). Embodiments of the invention provide a method for time offset alignment with PDV compensation where a synchronized frequency signal is available at a slave device via Synchronous Ethernet and is used to determine the compensation parameters for the PDV.

主权项

1. A method of synchronising the frequency and time of a slave clock in a slave device to a master clock in a master device, wherein the master device and the slave device are connected by an Ethernet network, the method including the steps of:
synchronising the frequency of the slave clock to that of the master clock using Synchronous Ethernet communications between the master device and the slave device; receiving in the slave device first and second timing messages sent from the master device and respective first and second timestamps being the time of sending of the first and second messages according to the master clock, and recording the time of receipt of the first and second messages according to the slave clock; calculating, via the slave device, forward variable delay encountered by the first and second messages in travelling from the master device to the slave device over the network by comparing the difference between the interval between the time of sending of said first and second messages and the interval between the time of receipt of said first and second messages; receiving in the master device third and fourth timing messages sent from the slave device and recording the time of receipt of the third and fourth messages according to the master clock; recording in the slave device the time of sending of the third and fourth messages according to the slave clock; sending the recorded time of receipt of the third and fourth messages to the slave device; calculating, via the slave device, reverse variable delay encountered by the third and fourth messages in travelling from the slave device to the master device over the network by comparing the difference between the interval between the time of sending said third and fourth messages and the interval between the time of receipt of said third and fourth messages; calculating, via the slave device, from the forward and reverse variable delays, a measure of noise associated with both the receipt of the first and second timing messages and receipt of third and fourth timing messages; estimating the variance of the measurement noise; and adjusting the actual time of the slave clock to synchronize it with the time of the master using the first and third timestamps, the recorded times of receipt of the first and third messages and the estimated variance.