Nortel Meridian 1 Option 11C, Администрирование и обслуживание

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Chapter 4 — Network clocking Page 143 of 492
Option 11C ISDN BRI Administration and Maintenance
— 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 C.O./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 guide to provide detailed Network
Synchronization, the following examples illustrate some of the basic concepts
to achieve stable clocking.
In Example 1, there is no digital connection to the local exchange.
Example 1
Isolated Private Network
553-7561.EPS
Master Clock source:
Non-tracking (Free run)
Clocking off Master:
Tracking on Primary
loop X
Option 11 Option 11
loop X loop X
LD 60
TRCK FRUN
LD 73:
PREF <cr>
SREF <cr>
LD 60
TRCK PCK
LD 73:
PREF loop X
SREF <cr>