Nortel Networks NN43001-301 - Manual (Page 50)

50 ISDN Primary Rate Interface equipment overview
Tracking mode In tracking mode, the DDP2 loop supplies an external
clock reference to a clock controller. Two DDP2 loops can operate in
tracking mode, with one defined as the primary reference source for clock
synchronization, the other defined as the secondary reference source. The
secondary reference acts as a back-up to the primary reference.
As shown in Figure 18 "Clock Controller primary and secondary tracking"
(page 50) , a system with dual CPUs can have two clock controllers (CC-0
and CC-1). One clock controller acts as a back-up to the other. The clock
controllers should be completely locked to the reference clock.
Figure 18
Clock Controller primary and secondary tracking
Free run (non-tracking) mode The clock synchronization of the system
can operate in free-run mode if:
• no loop is defined as the primary or secondary clock reference,
• the primary and secondary references are disabled, or
• the primary and secondary references are in local (near end) alarm
Nortel Communication Server 1000
ISDN Primary Rate Interface Installation and Commissioning
NN43001-301 02.03 Standard
Release 5.5 7 December 2007
Copyright © 2003-2007, Nortel Networks
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