Orolia Seven Solutions WR-ZEN Series, Руководство пользователя

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Figure 5-2:
FOCA algorithm under scenario 1
In t
1
, the active reference (solid green line) is WR1 because the primary reference
has reached a CRITICAL state (dashed red line).
In t
2
, the primary reference WR0 becomes available again (dashed green line) but
the device keeps using WR1 as the active reference as no failure has been detected
on this timing source.
In t
3
, an error is detected on WR1 and the FOCA algorithm will act differently accord-
ing to the configuration of its strategy.
A.
If the strategy is to re-evaluate all timing sources when a failure occurs, and
the primary reference is eligible, the WR0 will be selected as the active ref-
erence.
B.
If the strategy is to only fall-down, the FOCA algorithm will select the next
available timing source in the list and will thus lock on the external GNSS ref-
erence. With this strategy the only way to use back WR0 as the active ref-
erence is to restart the devices’ synchronization daemon (/etc/init.d/ppsi
restart) or to reach the last timing source and wait for a critical error.
Another key aspect of FOCA is how to determine when there is a “failure” on a timing
source. Some cases are obvious such as the link is down, no packets are exchange but
other cases can be more complex to identify: all these cases are detailed in the appendix
VCS code tables (
"Grand Master (GM VCS Code)" on page 142 ).
For a deeper understanding of the behavior of the FOCA algorithm it is recommend read-
ing the section
"Others" on page 146 in the appendix where more scenarios are detailed.
46
CHAPTER
5
•
WR-Z16 User Manual Rev. v3.4
5.1 Multi-sources & Resiliency