Nortel Networks Circuit Card 311 - Manual (Page 908)

908 NTAK20 Clock Controller daughterboard
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.
In tracking mode, one or more DTI/PRI cards supply a clock reference to the
NTAK20 clock controller daughterboard. When operating in tracking mode,
one DTI/PRI card is defined as the Primary Reference Source (PREF) for
clock synchronization. The other DTI/PRI card is defined as the Secondary
Reference Source (SREF). PREF and SREF are defined in LD 73.
There are two stages to clock controller tracking:
• tracking a reference
• locking on to 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 almost matched, the clock controller locks on to 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 on to it, and matches frequencies exactly. Occasionally,
environmental circumstances cause the external or internal clocks to vary.
When this happens, the internal clock controller briefly enters the tracking
stage. The green LED flashes until the clock controller is locked on to the
reference again.
If the incoming reference is unstable, the internal clock controller
continuously tracks, and the LED continuously flashes green. This condition
does not present a problem. It shows that the clock controller is continually
attempting to lock onto the signal. If slips occur, 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 outside
source. Instead, it provides its own internal clock to the system. This mode
can be used when the system acts as a master clock source for other
systems in the network. Free-run mode is undesirable if the system is
intended to be a slave to an external network clock. Free-run mode can
occur when both the primary and secondary clock sources are lost due to
hardware faults or invoked using software commands.
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
Copyright © 2003-2008, Nortel Networks
.