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5-24
SYNCHRONIZATION OF DIGITAL FACILITIES
DIGITAL TRANSMISSION FACILITY
PRIMARY FREQUENCY REFERENCE
SECONDARY (BACKUP) FREQUENCY REFERENCE
Figure 5-16. Less Than Optimal Diverse Routing
RULE 5:
Obtaining both primary and secondary synchronization facilities from within the same transmission
cable should be minimized.
RULE 6:
The total number of cascade node connections from the referenced node should be minimized.
EXAMPLE FOR RULE 6
Figure 5-17, Excessive Cascading, shows excessive cascading in that node B derives timing from a
source three transmission facilities away.
Figure 5-18, Minimized Cascading, shows less cascading in that node B derives timing from a source
two transmission facilities away. Excessive cascading is undesirable because of intermediate link
vulnerability. For example, an intermediate link failure in node C of figure 5-17, Excessive
Cascading, would cause node B to lose timing. Such a failure increases the number of slips between
nodes A and B. However, the same failure in Node C of figure 5-18, Minimized Cascading, does not
affect node B’s synchronization.