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SYNCHRONIZATION OF DIGITAL FACILITIES
5-21
RULE 2:
A node may use a facility as a backup only if the node at the other end is not using that same facility as
a backup.
EXAMPLE FOR RULE 2
Figure 5-13, Proper Use of Backup Facilities, illustrates an application of rule 2 and proper use of a
backup facility between nodes A and C.
DIGITAL TRANSMISSION FACILITY
PRIMARY FREQUENCY REFERENCE
SECONDARY (BACKUP) FREQUENCY REFERENCE
Figure 5-13. Proper Use of Backup Facilities
Figure 5-14, Improper Use of Backup Facilities, shows the same network arrangement but with
improper use of the backup facility between nodes A and C. This improper arrangement would form
a timing loop if node B should fail (nodes A and C would switch to their backup, which is each
other).
RULE 3:
The transmission facilities associated with those nodes meeting Rules 1 and 2 and having the greatest
availability must be selected for primary and secondary synchronization facilities.