Clocking Modes - Avaya Nortel Communication Server 1000 Reference

NTAK10 2.0 Mb DTI card
(switched on or off), the clock controller interface, in conjunction with software, enables or
disables the appropriate reference clock source.
The clock-controller circuitry on NTAK10 is identical to that of the NTAK20. While several DTI/
PRI packs can exist in one system, only one clock controller can be activated. All other DTI/
PRI clock controllers must be switched off.
Important:
Each Media Gateway that has a digital trunk must have a clock controller clocked to an
external reference clock.
Note:
Clocking slips can occur between systems that are clocked from different Central Offices
(COs), if the COs are not synchronized. The slips can degrade voice quality.

Clocking modes

The clock controller can operate in one of two modes: tracking or non-tracking (also known as
free-run).
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 , 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
508 Circuit Card Reference
Comments? infodev@avaya.com
July 2011