Nortel Networks Circuit Card 311 - Manual (Page 900)

900 NTAK10 2.0 Mb DTI card
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
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 primary recovers first, then the clock controller tracks to
the primary, but switches over to the secondary whenever the secondary
recovers. If the secondary recovers first, then the clock controller tracks
to the secondary.
A time-out mechanism prevents chatter due to repeated automatic switching
between primary and secondary reference sources.
See "Autorecovery and chatter" (page 915) .
Reference clock selection through software
The 2MB DTI card has the necessary hardware for routing its reference to
the appropriate line on the backplane.
Software is responsible for the distribution of the secondary references and
ensures that no contention is present on the REFCLK1 backplane line.
Software designates the 2MB DTI card as a primary reference source to the
clock controller. The secondary reference is obtained from another 2 Mbps
DTI card, which is designated by a craft person. No other clocks originating
from other 2MB DTI packs 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
timing signal. The clock controller uses either the two external/auxiliary
references or the 2MB DTI references.
The 2MB DTI card has the necessary hardware for routing its reference to
the appropriate line on the backplane
Software is responsible for the distribution of the secondary references and
ensures that no contention is present on the REFCLK1 backplane line.
Software designates the 2MB DTI Card as a primary reference source to
Nortel Communication Server 1000
Circuit Card Reference
NN43001-311 01.04 Standard
Release 5.0 23 May 2008
Copyright © 2003-2008, Nortel Networks
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