AT&T 7200 series, 7500 series, 7100 series, 2500 series manual Figure B-15.Optimal Diverse Routing

SYNCHRONIZATION OF DIGITAL FACILITIES B-23

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Facility rank ordering is generally based on limited technical and operational information. It is recommended that facility selections be based on local field experience where available.

RULE 4:

Where possible, the routes for all primary and secondary synchronization facilities should be diverse.

EXAMPLE FOR RULE 4

Figure B-15,Optimal Diverse Routing, explains the optimal configuration when rule 4 is used. Figure B- 16, Less Than Optimal Diverse Routing, shows a less than optimal application of rule 4.

A

D

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B

C

DIGITAL TRANSMISSION FACILITY

PRIMARY FREQUENCY REFERENCE

. . . . . . . . . . . . . . . . . SECONDARY (BACKUP) FREQUENCY REFERENCE

Figure B-15.Optimal Diverse Routing

Figure B-16,Less Than Optimal Diverse Routing, shows node C deriving both primary and secondary timing from node D, via the two separate T1 facilities. If node D should fail, node C would no longer receive timing that is traceable to node A. Here, node C would lose synchronization and begin to introduce slips into the network.