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B-12
SAMPLE INSTALLATION AND MAINTENANCE PROBLEMS
Digital CO Synchronization Problems
Synchronization of DS1 links into a digital CO presents far fewer problems. When a DS1/DMI
facility is connected directly into a digital interface circuit pack in the CO, then the only questions
are:
1.
2.
Is the CO reference (stratum clock) a stratum 3 or better?
Is that reference compatible with any other reference available to the System 75 or System 85?
Figure B-14. Compatible Synchronization References, shows this arrangement.
SYSTEM 75
OR SYSTEM 85
DIGITAL CO
DS1 OR DMI
STRATUM 3 OR BETTER
PRIMARY REFERENCE
DIGITAL CO
STRATUM 2 OR BETTER
Figure B-14. Compatible Synchronization References
This is an extreme example since most digital COs derive their timing from the AT&T standard
reference feequency. However, this example is a possibility when connecting to COs within smaller
LECs. Resolution of this type problem is to provide stratum-2 or better clocking to the other CO.
DACS
Synchronization with the digital access and cross-connect system (DACS) is generally straightforward.
A System 75 or System 85 will be synchronized to the DACS or higher-stratum clock. The only
caution is with the DACS customer-controlled reconfiguration. This reconfiguration permits the
customer to switch the DS1/DMI facility between other DS1 facilities at the DACS. During the
switching interval, it is possible for System 75 or System 85 to change from its primary reference to
its secondary reference, or even to its internal clock. If this should happen, it will only exist for a
short period of time before reverting back to the primary reference. This problem should not occur