5-26SYNCHRONIZATION OF DIGITAL FACILITIES

RULE 7:

The number of nodes receiving synchronization reference from any given node should be minimized.

EXAMPLE FOR RULE 7

Figure 5-19, 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 5-20,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.

DIGITAL TRANSMISSION FACILITY

PRIMARY FREQUENCY REFERENCE

SECONDARY (BACKUP) FREQUENCY REFERENCE

Figure 5-19.Excessive Synchronization from One Node

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AT&T DS1/DMi/ISDN-PRI manual Excessive Synchronization from One Node, 26SYNCHRONIZATION of Digital Facilities