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A-14
8700-A2-GB20-00April 2000
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.
Figure A-1 shows clocking in an LTU.
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
Figure A-1. System Timing
Figure A-2 shows sample system clock configurations.