Nortel 1000 Installation And Commissioning Manual page 70

70 ISDN Primary Rate Interface equipment overview
Figure 29
DDP cable for systems with an I/O panel
Clock
There are two types of clock operation - tracking mode and free-run mode.
Tracking mode
In tracking mode, the DDP loop supplies an external clock reference to a
clock controller. Two DDP 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.
Copyright © 2003-2007, Nortel Networks
.
Note: Since there exists several clock cabling options, none has been
represented in the diagram. Please refer to
72) for a description on each available option.
Nortel Communication Server 1000
ISDN Primary Rate Interface Installation and Commissioning
NN43001-301 02.03 Standard
Release 5.5 7 December 2007
"Clock configurations" (page