AT&T DEFINITY 7200 series - Manual (Page 234)

B-26 SYNCHRONIZATION OF DIGITAL FACILITIES
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RULE 7:
The number of nodes receiving synchronization reference from any given node should be minimized.
EXAMPLE FOR RULE 7
Figure B-19, Excessive Synchronization from One Node, shows an excess of synchronization from one
node. If transmission facility linking nodes A-B fails, then nodes B, D, E, and F will lose their
synchronization. However, if this same facility fails in figure B-20, Minimized Synchronization from One
Node, only nodes B, D, and E will lose synchronization. Node F remains synchronized to the network.
With few exceptions, it is not possible to engineer a synchronization network that will satisfy all seven
rules. In general, rules 1 through 3 apply in all cases. For rules 4 through 7, use those rules that apply to
your specific network and try to minimize outages based on the cases presented in the examples for each of
these rules.
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PRIMARY FREQUENCY REFERENCE
DIGITAL TRANSMISSION FACILITY
SECONDARY (BACKUP) FREQUENCY REFERENCE
F
C B
A
E
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D
Figure B-19. Excessive Synchronization from One Node