Version 6.6 523 October 2014
Installation & Operation Manual 38. Configuring the PSTN Subsystem
When all clock reference source links/trunks fail, the Timing Module functions as the
holdover clock source for up to 24 hours. The clock provided by the Timing Module
complies with STRATUM 3 (4.6ppm) requirements (for more information, see Section
'SA Synchronization and Alarm RTM' on page 69).
Figure
38-14: Timing Module Line Sync Clock Mode
When a clock source (OC-3/STM-1 link or E1/T1/T3 trunk) with a higher priority
returns in service after the failure, the Timing Module may either revert to the higher-
priority clock source or continue using the lower-priority clock source. The behavior is
controlled via the Auto Clock Reference Mode parameter.
When the Media Gateway board fails, the redundant Media Gateway board performs
switchover and takes control over the OC-3/STM-1 links or T1/E1/T3 trunks that were
connected to the failed board. When the Timing module fails, the redundant Timing
module performs switchover and takes control over the OC-3/STM-1 links or T1/E1/T3
trunks that were connected to the failed Timing module.
The Timing Module will switch to the next available clock reference source during the
switchover; however if the Auto Clock Reference Mode parameter is set to Auto
Revertive, it switches back to the previous “reference source” as soon as switchover is
complete.
38.8.3.1 Connecting the Media Gateway to the External Equipment
Connect OC-3/STM-1 links or E1/T1/T3 trunks to use as a clock reference source and
activate them (unlock corresponding entities). Use active Media Gateway boards only
and connect each clock reference source to a separate board.
View the Operational State of corresponding entity (trunk or link) at any time to verify
that the clock reference source connection is enabled.
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