Avaya Nortel Communication Server 1000 Reference page 532

NTAK79 2.0 Mb PRI card
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 CS 1000E, CS 1000M Cabinet,
and Meridian 1 PBX 11C Cabinetare used as a master clock source for other systems in the
network. Free-run mode is undesirable if the CS 1000E, CS 1000M Cabinet, and Meridian 1
PBX 11C Cabinetare intended to be a slave. It can occur, however, when both the primary and
secondary clock sources are lost due to hardware faults or when invoked by using software
commands.
Clock controller functions and features
The NTAK79 clock controller functions and features include:
• phase lock to a reference, generate the 10.24 MHz system clock, and distribute it to the
CPU through the backplane. Up to two references at a time are accepted
• primary to secondary switchover (auto-recovery is provided)
• prevent chatter
• error burst detection and correction, holdover, and free running capabilities
• compliance with 2.0Mb CCITT specifications
• software communication
• jitter filtering
• use of an algorithm to detect crystal aging and to qualify clocking information
Reference switchover
Switchover may occur in the case of reference degradation or reference failure. When
performance of the reference degrades to a point where the system clock is no longer allowed
to follow the timing signal, then the reference is said to be out of specification. If the reference
being used is out of specification and the other reference is still within specification, an
automatic switchover is initiated without software intervention. If both references are out of
specification, the clock controller provides holdover.
Autorecovery and chatter
If the software command "track to primary" is given, the clock controller tracks to the primary
reference and continuously monitors the quality of both primary and secondary references. If
the primary becomes out of specification, the clock controller automatically tracks to secondary
provided that it is within specifications. On failure (both out of specification), the clock controller
enters the HOLDOVER mode and continuously monitors both references. An automatic
switchover is initiated to the reference that recovers first. If the secondary recovers first, then
532 Circuit Card Reference
Comments? infodev@avaya.com
July 2011