Nortel Networks 1000 - Manual (Page 815)

Functional description 815
Switchover may occur in the case of reference degradation or loss of
signal. 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 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 occurs in the case of reference degradation or loss of signal.
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
out of specification. If the reference 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 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 goes out of specification, the
clock controller automatically tracks to secondary when the secondary
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, then switches over to the primary when the
primary recovers. If the primary recovers first, the clock controller tracks to
the primary and continues to do so even if the secondary recovers.
If the 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 goes out of
specification, the clock controller automatically tracks to primary provided
that 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 primary recovers first, the clock controller tracks to the
primary, but switches over to the secondary when the secondary recovers.
If the secondary recovers first, the clock controller tracks to the secondary
even if the primary recovers.
To prevent chatter due to repeated automatic switching between primary
and secondary reference sources, a time-out mechanism of at least 10
seconds is implemented.
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
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