Nortel Meridian 1 Option 11C, Administration And Maintenance

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Chapter 4 — Network clocking Page 151 of 492
Option 11C ISDN BRI Administration and Maintenance
There are two stages to clock controller tracking:
— tracking a reference, and
— locked onto a reference.
When tracking a reference, the clock controller uses an algorithm to match its
frequency to the frequency of the incoming clock. When the frequencies are
very near to being matched, the clock controller is locked onto the reference.
The clock controller will make small adjustments to its own frequency until
both the incoming and system frequencies correspond.
If the incoming clock reference is stable, the internal clock controller tracks
it, locks onto it, and matches frequencies exactly. Occasionally, however,
environmental circumstances cause the external or internal clocks to drift.
When this happens, the internal clock controller briefly enters the tracking
stage.
If the incoming reference is unstable, the internal clock controller is
continuously in the tracking stage. This condition does not present a problem,
rather, it shows that the clock controller is continually attempting to lock onto
the signal. If slips are occurring, however, it means that there is a problem
with the clock controller or the incoming line.
Free-run (non-tracking)
In Free-Run (Non-tracking) mode, the clock controller does not synchronize
on any source, it provides its own internal clock to the system. This mode can
be used when the Option 11 is used as a master clock source for other systems
in the network. Free-run mode is undesirable if the Option 11 is intended to
be a slave. It can occur, however, when both the primary and secondary clock
sources are lost due to hardware faults. It can also be turned on manually
using software commands.