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13 — System timing and timing sources
13-6 2902 MainStreet Technical Practices
90-2906-01 May 2002
Enabling a timing source
When a source is enabled, it becomes available to the system as a source of timing.
If an enabled source has a higher preference (lower class number) than the current
source of timing, the enabled source is automatically selected as the new source of
timing.
When a source is disabled, it becomes unavailable to the node as a source.
A timing source must be disabled before its configuration can be changed.
Selecting a timing source
When you select a timing source, it becomes the current source regardless of its class
number. Its status changes from Ready to Current.
When you deselect a source, its status changes from Current to Ready. The system
will then automatically select the Ready source with the highest preference (lowest
class number) to be the new current source.
Procedure 13-4 To enable and select a source
where source number is 1 or 2
13.3 Types of synchronization
Each timing source can be set for the following type of synchronization:
•
internal (FREE_RUN)
•
derived (DERIVED)
If the current timing source is lost or becomes degraded or if the SSU cannot
synchronize to it, the system automatically switches to the other source, providing it
has been configured and is available. If this source fails and the first source is still
unavailable, the system switches to its internal clock (free run).
ENABLE/DISABLE SELECT/DESELECT
CONFIG — SYNCH — SRC_NUMBER — < source number >
↵
SK000474
Note —
Free-run mode should be used only as a last resort because
the node is not fully synchronized with the network in this mode.