AT&T DS1/DMi/ISDN-PRI manual SYNCHRONIZATION-RELATED Problems

B-8SAMPLE INSTALLATION AND MAINTENANCE PROBLEMS

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SYSTEM 75/SYSTEM 85 OPTIONS:

●D4 FRAMING

●PER-CHANNEL SIGNALING

●ROBBED-BIT SIGNALING

●ZCS

DS1 OR DMI	TRANSMISSION FACILITY
INTERFACE

D4-CHANNEL BANK OPTIONS:

●D4 FRAMING

●PER-CHANNEL SIGNALING

●ROBBED-BIT SIGNALING

●ZCS

D4

CHANNEL

BANK

Figure B-8.System 75/System 85 to a D4-Channel Bank

Channels 1 through 24 may be used for almost any combination of trunks. Trunk compatibility is ensured by translating each channel to match the channel unit installed in the D4.

All trunks are translated in pairs, and the D4 must be equipped accordingly.

It is not advisable to use the spare slots in a channel bank for the storage of unused channel units.

SYNCHRONIZATION-RELATED PROBLEMS

Digital networking with customer-premises digital switches has placed new requirements for planning and evacuation on the network designer and installer. Each digital switch must now be synchronized to every other digital switch, digital CO (when applicable), and other DS1 transmission equipment. The NEC or REC should be involved in planning the network and at the same time come up with a network synchronization plan.

Synchronization is coordinated timing. A System 75 or System 85 digital switch and other DS1 transmission products all contain an internal timing source. The timing (clock) source conforms to standards of accuracy that place the clock in a category of accuracy (timing hierarchy). The lower the number of the stratum clock, the higher the accuracy. Therefore, a system with a stratum-4 clock would take its timing from a stratum 3 or a stratum 4, a stratum 3 from a stratum 2 or a stratum 3, and a stratum 2 from a stratum 1 or a stratum 2.

System 75, System 85, CEM, CDM, and D4-channel banks all have internal clocks of stratum-4 accuracy. The most basic rule of synchronization is that timing for all networked products is derived from the lowest-numbered clock connected (via DS1 facilities) to the device. Synchronization is not usually a problem when connecting (via DS1 facilities) to a digital CO. Synchronization problems occur most often in private networks; that is, those networks that do not have any DS1 connections to equipment outside the private network.