This article mainly from Calnex the CX5013 Time and Time error. In modern communication network architecture, time synchronization is very important. IEEE1588, ptp protocol is a standard protocol for time synchronization. This document discusses how time synchronization, time error how it affects network performance, and provide a way to weaken the corresponding time error to ensure the accuracy of time.
1. What is time?
Time is a basic physical concepts of space and time metrics fourth dimension, that allows the past to the present to the future to arrange the event. In the electronic system that allows sorting events into a series of steps, or to multiple devices to share resources, we need to measure time. As for the time of origin of the physical problems, too esoteric, limited knowledge, temporarily not discussed.
1.1 Time and Frequency
In order to measure time, we need the concept of some fixed period of time. Is repeated within a fixed period of a regular event, which is the concept of frequency. Historically, the solar day is used to measure the elapsed time. Early social scientists need to divide the number of components per day. For example, Egyptians used daylight for 10 hours plus 2 hours to complete a day late. The problem with this method is to measure the length of each hour with the seasons change. Later, by noon to noon, divided into equal 24 hours to solve the problem.
There are many physical event may represent a fixed period; astronomical repetition period, for example day, year, lunar months; pendulum motion physical events such resonance, quartz or cesium atom. These time measurements are used in some form.
1.2 Properties of the relative time
Because time itself is a basic physical dimensions, measure time is relative. We need to know the measure of the start time or era of time. For example, different systems use different calendars to determine the date of the beginning of the event; the Romans began to build from Rome to calculate the years; Gregorian calendar adopted Jesus' birth date as a start. Islamic chronology is black Chi pull (Hijra) for the era of Muharram .