7/27/2023 0 Comments Clockx x64After some time, small offsets (significantly less than a second) will be slewed (adjusted slowly), while larger offsets will cause the clock to be stepped (set anew). In the latter case the operation system’s clock will continue with the last corrections effective while the new reference time is being rejected. For a tiny offset ntpd will adjust the local clock as usual for small and larger offsets, ntpd will reject the reference time for a while. Instead, ntpd’s reaction will depend on the offset between the local clock and the reference time. Therefore, NTP has no special methods to handle the situation. Once synchronized, there should not be any unexpected changes between the clock of the operating system and the reference clock. Ideally the reference time is the same everywhere in the world. Servers may send out the time using multicast or broadcast addresses.Servers can send the time directly to a peer.Servers to be polled can be configured manually.There are serveral ways an NTP client knows which NTP servers to use: Each NTP server maintains an estimate of the quality of its reference clocks and of itself. Among these values are: offset (or phase), jitter (or dispersion), frequency error, and stability. NTP will compute some additional statistical values that describe the quality of time it sees. Each system that has its time synchronized to some reference clock can also be a time reference for other systems, but the stratum will increase for each synchronization.Ī reference clock will provide the current time. In NTP these time references are named stratum 0, the highest possible quality. Less expensive (and accurate) reference clocks use one of the terrestrial broadcasts known as DCF77, MSF, and WWV. These satellites in turn have a cesium clock that is periodically corrected to provide maximum accuracy. A typical example would be a GPS (Global Positioning System) receiver that gets the time from satellites. Cheaper, and thus more popular, clocks are receivers for some time signals broadcasted by national standard agencies. Typical candidates for reference clocks are very expensive cesium clocks. The special thing about these things is accuracy: reference clocks must accurately follow some time standard. The focus in this section is on theory.ĥ.1.1.2 How will NTP use a reference clock?ĥ.1.1.3 How will NTP know about Time Sources?ĥ.1.1.4 What happens if the Reference Time changes?ĥ.1.2.2 Which Network Protocols are used by NTP?ĥ.1.3.2 How frequently will the System Clock be updated?ĥ.1.3.3 How frequently are Correction Values updated?ĥ.1.3.4 What is the Limit for the Number of Clients?ĥ.1.4.2 How are Synchronization Loops avoided?ĥ.1.5.1 What is the allowed range for minpoll and maxpoll?ĥ.1.5.2 What is the best polling Interval?ĥ.1.6.1 How will NTP discipline my Clock?ĥ.1.1 Time References 5.1.1.1 What is a reference clock?Ī reference clock is some device or machinery that spits out the current time. To help understand the details of planning, configuring, and maintaining NTP, some basic concepts are presented here. This section will try to explain how NTP will construct and maintain a working time synchronization network.
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