Nortel Networks 1000 - Manual (Page 808)

808 NTAK20 Clock Controller daughterboard
When this happens, the internal clock controller briefly enters the tracking
stage. The green LED flashes momentarily until the clock controller is
locked on to 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.
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
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
.