Tracking Mode - Avaya Nortel Communication Server 1000 Reference

Tracking mode

In tracking mode, one or more DTI/PRI cards supply a clock reference to the 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 CS 1000 acts
as a master clock source for other systems in the network. Free-run mode is undesirable if the
CS 1000 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.
Circuit Card Reference
Introduction
July 2011 587