Nortel Networks Circuit Card User Manual

 NT5D97 Dual-port DTI2/PRI2 card

There are two types of clock operation - tracking mode and free-run 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.

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