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A. Configuration Options
A-16
May 2002 8700-A2-GB20-40
When a system clock source fails or is misconfigured, an alarm is reported.
Secondary clock failures are not reported unless the primary clock has also failed.
When the primary clock fails, clocking is switched to the secondary clock source, if
available. If a secondary clock is not available, the clock switches to secondary
holdover mode. In holdover mode, the system attempts to generate timing which is
consistent with the last clock reference. A switch is made back to the primary clock
when it becomes available. Holdover mode is meant to be used for short durations
while network synchronization is temporarily disrupted. The switch back to
primary/secondary clock is made when they become available again.
Figure A-1, System Timing, shows clocking in an LTU.
Figure A-1. System Timing
Figure A-2, System Clock Configuration Examples, shows sample system clock
configurations.
Cross-Connect
Framer
DSX-1/
G.703
Driver
Framer
DSL
Transceiver
System
Timing
Module
DSX-1/G.703 Port
Internal Oscillator
System Timing
99-16627