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SYNCHRONIZATION OF DIGITAL FACILITIES B-7
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NOTE: For System 85 and Generic 2, the SCS provides a stratum-4 clock.
However, a stratum-3 external clock may be used instead of the SCS.
LEGEND
NOTE
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AT&T STANDARD REFERENCE FREQUENCY
DSO DSO DSO
DCO DCO
DACS
D4
SYSTEM
85
CEM
SYSTEM
75
SYSTEM
85
DEFINITY
G1 OR G2
DEFINITY
G1 OR G2
SYSTEM
75 OR 85
SECONDARY FREQUENCY REFERENCE
PRIMARY FREQUENCY REFERENCE
DIGITAL TRANSMISSION FACILITY
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STRATUM 4
STRATUM 3
STRATUM 2
STRATUM 1
Figure B-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 B-4, SCS (Generic 2), shows the SCS circuit pack.