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SYNCHRONIZATION OF DIGITAL FACILITIES
5-7
LEGEND
DIGITAL TRANSMISSION FACILITY
PRIMARY FREQUENCY REFERENCE
SECONDARY FREQUENCY REFERENCE
NOTE: For System 85 and Generic 2, the SCS provides a stratum-4 type-II clock.
However, a stratum-3 external clock may be used instead of the SCS.
Figure 5-3. Stratum Levels for the Synchronization Hierarchy
System 85 and Generic 2 Synchronization Architecture
Both System 85 and Generic 2 can function as either a timing slave or timing master. As a slave, the
switch receives digital data from one or two DS1s. One interface supplies the primary
synchronization reference and the other interface supplies the secondary reference. The timing source
selected is determined by the system clock synchronizer (SCS) TN463 circuit pack and
synchronization software. The SCS synchronizes (phase locks) to either the primary reference,
secondary reference, or the internal high-accuracy clock. Figure 5-4, SCS (Generic 2), shows the SCS
circuit pack.