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What is stratum in NTP; why is it shown in the TR7 Time Info row?
Short answer
Stratum is the level that shows how many steps a clock is away from the reference time source (RFC 5905): a server directly connected to a reference clock such as an atomic clock or a GPS receiver is stratum 1, a server synchronized from it becomes stratum 2, and the number increases by one at each step; the smaller the number, the closer it is to the reference. In the Time Info row found on the TR7 NTP Time Sync screen and in the Device Info panel on the Summary tab of the home page (Home), the name of the server the device is actually synchronized with at that moment, the clock offset and, in parentheses, the Stratum value are shown. This value is the stratum level of the device clock itself; it is one more than the stratum of the server the device is synchronized with (e.g. a TR7 synchronized to a stratum 2 server shows Stratum 3). The server name may not be the value entered in the NTP Server field: when a pool address (e.g. tr.pool.ntp.org) is entered, the concrete server that the pool selected at that moment appears, and it can change over time.
Where It Is Used in TR7
| Where | Field / label | What for |
|---|---|---|
| Settings → General Settings → NTP Time Sync | Time Info → server name, clock offset and "(Stratum N)" | Seeing the synchronized source and the stratum level of the device; separate for each device in a cluster |
| Home → Summary → Device Info panel | Time info row | The same information on the home page; a separate column for each device in a cluster |
| Settings → General Settings → NTP Time Sync → Edit | NTP Server, Minimum Agreeing Time Sources | Determining the sources to synchronize with and the minimum number of sources that must agree |
- Time info example: if the device is synchronized, it reads "
<device name>is faster / slower than NTP server<server>(Stratum N) by X seconds"; if there is no synchronization, it reads "Cannot synchronize with NTP server". - Stratum shows only the position in the chain; the accuracy is determined separately by the clock offset and the agreement of the sources with one another.
Common Misconceptions
- "As the stratum value gets smaller, the clock gets worse." On the contrary; a small stratum means being closer to the reference source.
- "The Stratum in parentheses is the level of the synchronized server." The value is the level of the device itself; the level of the server is one less than this.
- "The server name in Time info is the address I entered." If a pool address or multiple servers were entered, the concrete server selected at that moment appears.
How it is done in the documentation
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