Nortel Networks 311 Holdover and free-run, Reference clock selection through software

Architecture 951
A time-out mechanism prevents chatter due to repeated automatic switching
between primary and secondary reference sources.
See "Autorecovery and chatter" (page 915).
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 917).
Reference clock selection through software
The NTAK79has the necessar y hardware forrouting its reference to the
appropriate line on the backplane.
The software is responsible forthe distribution of the secondar y references
and ensures that no contention is present on the REFCLK1 backplane line.
The software designates the NTAK79as 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 NTAK79circuit 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 refersto an auxiliar y timing source whichis 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 01.04 Standard
Release 5.0 23 May 2008
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