SEVEN WR-Z16, Руководство пользователя

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Chapter 5: Timing
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v3.3-a 12/07/2022
of PTP+SyncE as timing source, allows to re-distribute timing using WR without
significant penalties.
NTP Timing source (Survey mode)
Due to its poor accuracy, NTP protocol 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. Section
§0 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 t
he “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 appears in
the network. It also enforces the evaluation of the timing sources in a rank order configured by
the user.
FOCA algorithm has been designed to provide a “safer” approach
than BMCA or even
ABMCA (Alternate BMCA) to handle switching between multi-references. Its main characteristics
are:
•
Provides a deterministic behavior.
•
Does not allow a new (rogue) node to become the active reference.
•
Recovers back to normal state must be done under the supervision of an operator.
•
Allows switching between cross WR/PTP profiles and multiple external timing sources.
•
Has been designed with tree network topology in mind and it is not optimized for ring
topology.
The Figure depicts a configuration where the first two timing sources are employing WR protocol,
followed by an external GNSS receiver connected to the front panel reference (GM) and finally