Nortel Networks 553-3001-211 manual Architecture, Clock operation, Tracking mode

NT5D97 Dual-port DTI2/PRI2 card Page 341 of 894

Table 133

Switch setting for MSDL external card (Part 2 of 2)

		Switch Setting
DNUM (LD 17)	1	2	3	4
13	ON	OFF	ON	ON
14	OFF	ON	ON	ON
15	ON	ON	ON	ON

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 74, 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

Circuit Card Description and Installation