AT&T DS1/DMi/ISDN-PRI manual Digital CO Synchronization Problems, Dacs

B-12SAMPLE 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 . Is the CO reference (stratum clock) a stratum 3 or better?

2 . 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

DS1 OR DMI

PRIMARY REFERENCE

DIGITAL CO

STRATUM 3 OR BETTER

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