Nortel Networks 1000 - Manual (Page 851)

Architecture 851
A time-out mechanism prevents chatter due to repeated automatic
switching between primary and secondary reference sources.
See “Autorecovery and chatter” (page 815) .
Holdover and free-run
In the temporary absence of a synchronization reference signal, or when
sudden changes occur on the incoming reference due to error bursts, the
clock controller provides a stable holdover. The free-run mode is initiated
when the clock controller has no record of the quality of the incoming
reference clock.
If the software command "free run" is given, the clock controller enters the
free-run mode and remains there until a new command is received. Note
that the free-run mode of operation is automatically initiated after the clock
controller is enabled.
In the temporary absence of a synchronization reference signal, or when
sudden changes occur on the incoming reference due to error bursts, the
clock controller provides a stable holdover. The free-run mode is initiated
when the clock controller has no record of the quality of the incoming
reference clock.
If the software command "free run" is given, the clock controller enters the
free-run mode and remains there until a new command is received. Note
that the free-run mode of operation is automatically initiated after the clock
controller is enabled.
See “Holdover and free-run” (page 817) .
Reference clock selection through software
The NTAK79 has the necessary hardware for routing its reference to the
appropriate line on the backplane.
The software is responsible for the distribution of the secondary references
and ensures that no contention is present on the REFCLK1 backplane line.
The software designates the NTAK79 as the primary reference source to
the clock controller. The secondary reference is obtained from another
NTAK79 card, which is designated by a technician. No other clocks
originating from other NTAK79 circuit cards are used.
The clock controller provides an external timing interface and is capable
of accepting two signals as timing references. In this case, an external
reference refers to an auxiliary timing source which is bridged from a traffic
carrying signal. This is not intended to be a dedicated non-traffic bearing
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 02.06 Standard
27 August 2008
Copyright © 2003-2008 Nortel Networks
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