G
LOSSARY AND
A
BBREVIATIONS
8030HEPTA/GPS GPS - NTP Time Server with 2x 10/100/1000 MBit LAN Interface - V04.00
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14
Glossary and Abbreviations
14.1 NTP-specific Terminology
Stability
The average frequency stability of the clock system.
Accuracy
Specifies the accuracy in comparison to other clocks.
Precision of a clock
Specifies how precisely the stability and accuracy of a
clock system can be maintained.
Offset
This value represents the time difference between two
clocks. It is the offset by which the local time would have to
be adjusted in order to keep it congruent with the reference
clock.
Clock skew
The frequency difference between two clocks
(first derivative of offset over time).
Drift
Real clocks vary in frequency difference (second derivative
of offset over time). This variation is known as drift.
Roundtrip delay
Roundtrip delay of an NTP message to the reference and
back.
Dispersion
Represents the maximum error of the local clock relative to
the reference clock.
Jitter
The estimated time error of the system clock measured as
the average exponential value of the time offset.
14.2 Tally Codes (NTP-specific)
space
reject
Rejected peer
– either the peer is not reachable or its syn-
chronization distance is too great.
x
falsetick
The peer was picked out by the NTP intersection algorithm
as a false time supplier.
.
excess
The peer was picked out by the NTP sort algorithm as a
weak time supplier on the basis of synchronization distance
(concerns the first 10 peers).
-
outlyer
The peer was picked out by the NTP clustering algorithm
as an outlyer.
+
candidate
The peer was selected as a candidate for the NTP combin-
ing algorithm.
#
selected
The peer is of good quality but not among the first six peers
selected by the sort algorithm on the basis of synchroniza-
tion distance.
*
sys.peer
The peer was selected as a system peer. Its characteristics
are transferred to the Base System.
o
pps.peer
The peer was selected as a system peer. Its characteristics
are transferred to the Base System. The current synchroni-
zation is derived from a PPS (pulse-per-second) signal ei-
ther indirectly via PPS reference clock driver or directly via
kernel interface.
