Nortel Networks 1000 - Manual (Page 807)

Introduction 807
Tracking mode
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.
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 very near to being matched, the clock controller is locked 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 onto it, and matches frequencies exactly. Occasionally, however,
environmental circumstances cause the external or internal clocks to drift.
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
.