AT&T 7100 series, 7500 series, 2500 series External-Reference Selection Rules, Rules 2 Through

	SYNCHRONIZATION OF DIGITAL FACILITIES		B-27
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	DIGITAL TRANSMISSION FACILITY
	PRIMARY FREQUENCY REFERENCE
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Figure B-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 B-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, external stratum-3 clock, and HAC) and external-reference selections.