Chapter 5:
Timing
97
v3.3-a 12/07/2022
2.
Learning:
In order to maintains the best accuracy during enough time the holdover is
learning about its environment using adaptative algorithms. This learning period has been
set to 3 days in order to ensure to fulfill the accuracy specifications.
a.
If the holdover is triggered before this learning time, it will directly enter the
expired state.
3.
Ready:
Once the HO has learned enough time to ensure good performance, the HO will
be ready to be triggered at any moment (it will continue learning to slightly improve its
performance).
4.
Activated:
The holdover has been triggered (by trigger_origin) and it is actually being the
active timing source of the device. The clock info will be modified accordingly and
announced to the timing network.
5.
Expired:
Reaching the holdover expired state means that the device announce itself with
a Free-Running clock_class and a clock_accuracy to UNKNOWN. This also means that the
corresponding VSC code is CRITCAL and thus if a better timing source is detected it will
switch to this one. Worth mentioning that during the expired state, the holdover timing
source is using the OCXO oscillator that provides better performance than the internal
onboard oscillator.
Holdover and FOCA
As mentioned above FOCA only switches between timing source when a failure is
detected. This mean that if the active timing source of a device is HO, it will stick to it
until reaching the expired states (Failure state of HO).
GNSS reference to discipline the HO
The holdover adaptative algorithms have been optimized to learn from a GNSS
reference clock (GPS L1 signals). A better clock can be used as reference (e.g., Atomic
Clock, ePRTC, multi bands/constellations GNSS receiver) but using a clock reference
with worth performance might not fulfil the provided specifications.
5.8.1 Configuration
The configuration of the holdover is easy and can be leaved untouched. However, depending on
the user needs and the boundaries for timing accuracy, the Time to expired value should be
adjusted to meet its specifications.
OID
Name
Value Type
Description
3.7210.x
holdover/cfg/xxx
Configuration for the Holdover if available
3.7210.0 Source Rank
<Integer>
Default: 0
Source rank of the holdover as timing source. If
leaved at zero it will be always placed as the last
