Nortel Circuit Card, Installation Manual, Page: 353 / 908

NT5D97 Dual-port DTI2/PRI2 card Page 353 of 906
Circuit Card Description and Installation
Architecture
Clock operation
There are two types of clock operation - tracking mode and free-run mode.
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 77, 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.
Free run (non-tracking) mode
The clock synchronization of the 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
13 ON OFF ON ON
14 OFF ON ON ON
15 ON ON ON ON
Table 138
Switch setting for MSDL external card (Part 2 of 2)
Switch Setting
DNUM (LD 17) 1 2 3 4