Version 6.6 519 October 2014
Installation & Operation Manual 38. Configuring the PSTN Subsystem
38.8.2 Timing Module BITS Sync Clock Mode
In Timing Module BITS Sync clock mode, all Media Gateway boards are synchronized
by two BITS Generators (Building Integrated Timing Source) trunks. These trunks are
synchronized with the Media Gateway boards via two SA-1/RTMs, each with a
designated timing module. Two SA-1/RTMs are required to ensure seamless clock
operation in case of failure of one of the SA-1/RTMs modules.
Note: To activate the Timing Module BITS Sync clock mode, you must order SA-
1/RTMs (SA/RTM with a resident Timing Module). To order the Media Gateway
with this module, see the AudioCodes price list.
When one of the reference clock sources (BITS Generator) fails, the Timing Module
automatically switches to another source and continues using it as a reference clock
for the whole Media Gateway.
Automatic failover of the BITS Generator clock source can be disabled by configuring
the Selector Mode parameter to Manual (see table below). In the manual mode, the
Timing Module will always use the clock source with a higher priority, even when this
source fails. The manual mode is primarily intended for the lab usage and is not
recommended for field deployments.
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/RTM Synchronization and Alarm Rear Transition Module' on page 69).
Figure
38-13: Timing Module BITS Sync Clock Mode
When both BITS trunks fail, the Timing Module continues to function as the clock
("clock holdover") for up to 24 hours. The clock provided by the Timing Module
complies with STRATUM 3 (4.6ppm) requirements.
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