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SYNCHRONIZATION OF DIGITAL FACILITIES
5-27
DIGITAL TRANSMISSION FACILITY
PRIMARY FREQUENCY REFERENCE
SECONDARY (BACKUP) FREQUENCY REFERENCE
Figure 5-20. Minimized Synchronization from One Node
External-Reference Selection Rules
There are seven rules for selecting external synchronization references. These rules are described
next.
RULE 1:
Nodes within the externally referenced sublevel may not use as a reference source a facility from a
node within the internally referenced sublevel (refer to figure 5-11, External and Internal Reference
Levels, for an explanation of these terms).
RULES 2 THROUGH 7:
Rules 2 through 7 are the same for both internal- (that is, SCS and HAC) and external-reference
selections.