Lucent Technologies MERLIN LEGEND Release 5.0 Feature Reference page 503

MERLIN LEGEND Communications System Release 5.0
Feature Reference 555-650-110
Features
Primary Rate Interface (PRI) and T1
In the event of a maintenance failure of primary synchronization, backup
synchronization can be provided by secondary and tertiary clock synchronization.
In addition, the source of synchronization is factory-set to Loop Clock Reference
Source so that the clock is synchronized to the outside source. With a 100D
module, it can be set to Local Clock Reference Source so that the clock is
free-running. However, this is not recommended for most permanent installations
and systems with Primary Rate Interface (PRI). This setting must be made for the
primary, secondary, and tertiary synchronization sources.
The following lists the options for primary, secondary, and tertiary clock
synchronization sources in order of preference:
1. The clock sources on BRI ports with DSLs in service. If at all possible, all
three clock sources should be on the same 800 NI-BRI module. If they are
not, interruptions in high-speed data calls can occur when the clock source
switches to a backup source.
2. The loop clock source on any 100D module.
3. The loop clock source on any 100D module in T1 mode emulating tie
trunks.
4. The local clock source on any 100D module.
NOTE:
Ports that are not in service should never be programmed as clock
sources.
Clock Switching
When the primary clock source is not able to provide the system clock, the
secondary clock source is used if it exists and is capable of providing the system
clock. If the secondary clock source is incapable of providing the system clock,
the tertiary clock source is used.
If none of these is capable of providing the system clock, the communications
system searches 800 NI-BRI and 100D modules for a clock source, starting from
the first module in the system and ending with the last module. The clock is
chosen with the following order of preference:
1. Loop clock source on an 800 NI-BRI or 100D module.
2. Local clock source on an 800 NI-BRI or 100D module.
3. Local clock source on the processor module.
Issue 1
June 1997
Page 471
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