Nortel Networks 1000 - Manual (Page 795)

Architecture 795
If the incoming reference is unstable, the internal clock controller remains
continuously in the tracking stage with the LED flashing green all the
time. 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 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 , Cabinet systemare used as
a master clock source for other systems in the network. Free-run mode
is undesirable if the CS 1000E, Cabinet systemare intended to be a
slave. It can occur, however, when both the primary and secondary clock
sources are lost due to hardware faults or when invoked by using software
commands.
Tracking mode 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 makes 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. The green LED flashes momentarily until the clock controller is
locked onto the reference once again.
If the incoming reference is unstable, the internal clock controller remains
continuously in the tracking stage with the LED flashing green all the
time. 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 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 11C is used as a master clock
source for other systems in the network. Free-run mode is undesirable if
the Option 11C is intended to be a slave. It can occur, however, when both
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
.