AT&T DS1/DMi/ISDN-PRI manual External-Reference Selection Rules, Rules 2 Through

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.