Glossary
Stratum Definition
1 Primary server
2-15 Secondary server
16-255 Unsynchronized, unreachable.
For example, the SyncServer is:
n stratum 1 when the Hardware Clock (stratum 0) is synchronized to an input reference, in
holdover mode, or in freerun mode.
n stratum 2 through 15 when it is synchronized to a remote NTP server.
n stratum 16 when it is unsynchronized, indicating that it is searching for a valid source of
timing information.
The settings on the NTP - Prefs (on page 50) page affect stratum behavior.
Poll Exponent
This is an eight-bit signed integer representing the maximum interval between successive
messages, in seconds, to the nearest power of 2. The values can range from 4, indicating a
poll interval of 16 seconds, to 17, indicating a poll interval of 131,072 seconds (~36.4 hours).
Precision
This is an eight-bit signed integer representing the precision of the system clock, in seconds,
to the nearest power of 2. For instance, a value of −18 corresponds to a precision of about
one µs. The precision is normally measured by NTP at startup and is defined as the minimum
of several iterations of the time to read the system clock.
Root Delay
This is a 32-bit unsigned fixed-point number indicating the total roundtrip delay to the ref-
erence clock, in seconds, with the radix point between bits 15 and 16. This value is always
positive.
Root Dispersion
This is a 32-bit unsigned fixed-point number indicating the maximum error relative to the ref-
erence clock, in seconds, with the radix point between bits 15 and 16. This value is always
positive.
Reference Identifier
This is a 32-bit code identifying the particular server or reference clock. The interpretation
depends on the value in the stratum field. For stratum 1 (reference clock) this is a four-octet,
left-justified, zero-padded ASCII string assigned to the radio clock. The following have been
used as ASCII identifiers:
GOESGeosynchronous Orbit Environment Satellite
GPSGlobal Positioning System
PPSGeneric pulse-per-second
IRIGInter-Range Instrumentation Group
WWVBLF Radio WWVB, Ft. Collins, CO, 60 kHz
Page 200..........................................................................997-01520-02 Rev. F1
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