AT&T DS1/DMi/ISDN-PRI manual

5-8SYNCHRONIZATION OF DIGITAL FACILITIES

BACKPLANE CABLE TO PRIMARY DS1 INTERFACE (NOTE)

BACKPLANE

CABLE TO

SECONDARY DS1

INTERFACE (NOTE)

STRATUM 4

HIGH ACCURACY

CLOCK

PRIMARY

REFERENCE

SECONDARY

REFERENCE

TN463 CIRCUIT PACK

M A I N

PHASE

LOCKED

L O O P

MODULE

CONTROL

O R TMS CLOCK OSCILLATOR

OPTIONAL CROSS-COUPLED CABLE FROM DUPLICATED SCS

NOTE: These cables should not be installed if the switch is the master timing source for the network.

Figure 5-4.SCS (Generic 2)

Typically, the switch will be equipped with several DS1 circuit packs. The DS1 that is selected as the primary or secondary reference is dependent on the internal cable configuration and administration details. Here, each System 85 or Generic 2 that is configured with at least one DS1 requires a SCS, including the master node. Unless synchronized to the network and not the stratum-3 or stratum-4 clock, the master node will not have the primary and secondary synchronization cables.

A System 85 or Generic 2 may consist of either a single-module or multimodule architecture. Typically, the switch architecture is unduplicated, but it may also be duplicated for critical reliability applications. The switch architecture determines the equipment carriers that will contain the SCS circuit packs.

For single-module applications, the SCS is located in the module control carrier. In addition to the SCS, a module clock is also required. The SCS controls the module clock. For multimodule applications, the SCS is located in the time-multiplexed switch (TMS) carrier and controls the TMS clock oscillator.

When the switch architecture is duplicated, the synchronization components and cables will also be duplicated. For duplicated systems, functioning modules are called online, while backup modules are called offline. The offline SCS phase locks to the cross-coupled clock signal from the online SCS. In