Meridian Nortel 1 Option 11C Technical Reference Manual page 489

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 may be accepted.
• provide primary to secondary switchover (auto-recovery is provided)
• prevent chatter
• provide error burst detection and correction, holdover, and free running
capabilities
• comply with 2.0Mb CCITT specifications
• communicate with software
• provide jitter filtering
• make use of an algorithm to aid in detecting 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 will be 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 the clock controller tracks to the
secondary, but switches over to the primary when the primary recovers. If the
primary recovers first, the clock controller tracks to the primary.
NTAK79 2.0 Mb PRI card
Option 11C and 11C Mini
Page 489 of 544
Technical Reference Guide