Nortel Networks 1000 - Manual (Page 797)

Architecture 797
•
providing error burst detection and correction, holdover, and free
running capabilities
•
complying with 2.0 Mb CCITT specifications
• communicating with software
• filtering jitter
•
making 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 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.
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
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
whenever the primary recovers. If the primary recovers first, then the clock
controller tracks to the primary.
If the software command "track to secondary" is given, the clock controller
tracks to the secondary reference and continuously monitors the quality of
both primary and secondary references. If the secondary becomes out of
specification, the clock controller automatically tracks to primary provided
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
.