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-ref-
erences. 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 following figure depicts a configuration where the first two timing sources are employ-
ing WR protocol, followed by an external GNSS receiver connected to the front panel ref-
erence (GM) and finally ending with the holdover to slowly drift until corrective
maintenance. It also illustrates how the two strategies of the FOCA algorithm behave.
Figure 5-1: Multi-timing sources handle by FOCA policy with its two strategies: only fall-down
(blue) & re-evaluation (purple)
An example of the behavior is given by the scenario illustrated in the next image where the
following events are shown:
5.1 Multi-sources & Resiliency
CHAPTER 5 • WR-Z16 User Manual Rev. v3.4
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