5.1 Multi-sources & Resiliency
To ensure continued operation over possible failures, the WR-Z16 incorporates an innov-
ative system that handles multiple timing sources. It also synthesizes these timing sources
into a simplified state (a.k.a Virtual Clock State) to ease the monitoring of the device and
distributes a common timing information to the down layers.
5.1.1 Timing Sources
The WRZ-OS can handle multiple timing sources in order to discipline the local oscillator of
the device. These timing sources can be of different types:
External Reference (Front panel connectors)
White Rabbit (High-Accuracy PTP)
NTP (Survey mode only) → Coming soon!
Holdover (Always used as last timing source if available)
Note: PTP as timing source: A pure PTP timing source (slave) should not be
selected if the timing is then re-distributed using WR (master). Indeed, the
jittered correction run by PTP clock is not compatible with the precision
needed for WR/HA distribution. However, a combination of PTP+SyncE as
timing source, allows to re-distribute timing using WR without significant
penalties.
Note: NTP Timing source (Survey mode): Due to its poor accuracy, NTP pro-
tocol is always in Survey Mode and thus cannot actively discipline the local
clock.
Then, a maximum total of 5 timing sources of the same or different types can be handled.
"FOCA: The Failover Clock Algorithm" below details the common parameters shared by
all the timing sources and how they are used to determine their states.
5.1.2 FOCA: The Failover Clock Algorithm
The FOCA has been designed for the purpose of automatically switching from one timing
source to another by applying the following policy:
In case of failure of the active timing source, switch to the next ready timing source.
This algorithm is based on the “Best Master Clock Algorithm (BMCA)” detailed in the PTP
IEEE 1588-2019 standard but acts only in case of failure and not when the “best” source
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CHAPTER 5 • WR-Z16 User Manual Rev. v3.4
5.1 Multi-sources & Resiliency
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