Reference switchover, Autorecovery and chatter – Nortel Networks 1000 User Manual

Page 849

Architecture

849

•

provide jitter filtering

•

make use of an algorithm to aid in detecting crystal aging and to qualify
clocking information

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.

See

“Reference switchover” (page 814)

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

Nortel Communication Server 1000

Circuit Card Reference

NN43001-311

02.06

Standard

27 August 2008