AT&T Telephone DS1/DMi/ISDN-PRI Bedienungsanleitung PDF herunterladen (Seite 117)

100

101

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.

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