Nortel Communication Server 1000S Installation And Configuration Manual page 200

Page 200 of 394
553-3001-201 Standard 2.00
Clock Controller description and installation
• The source should not be in free-run itself (providing its own clock)
unless it is operating in a fully independent network where the source
acts as a Master (see "Plesiosynchronous operation" on
• When connecting two PBXs together (no CO connections), the most
reliable PBX should be the Master. Reliability here refers to Dual
CPU/Dual Clock, battery back-up or stratum level of the clock controller.
• Avoid timing loops. A timing loop occurs when a clock using as its
reference frequency a signal that it itself traceable to the output of that
clock. The formation of such a closed timing loop leads to frequency
instability and is not permitted. Timing loops are sometimes unavoidable
on the secondary clock reference source.
• Ensure all CO/PBX links used as clock references have a traceable path
back to the same stratum 1 clock source.
While it is beyond the scope of this discussion to provide detailed Network
Synchronization, the following examples illustrate some of the basic concepts
to achieve stable clocking.
Figure 60
Example 1, Isolated Private Network
Small System
LD 60
TRCK FRUN
LD 73:
PREF <cr>
SREF <cr>
Master clock
Master Clock source:
Non-tracking (Free run)
In this example, there is no digital connection to the Central Office.
September 2004
loop X
page 195.)
Small System
LD 60
loop X
TRCK PCK
LD 73:
PREF loop X
SREF <cr>
Slave
Clocking off Master:
Tracking on Primary
loop X
553-AAA0083