Figure B-3. Stratum Levels For The Synchronization Hierarchy - AT&T DEFINITY 2500 series Network Manual

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AT&T STANDARD REFERENCE FREQUENCY
DSO
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DEFINITY
G1 OR G2
DEFINITY
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SYSTEM
G1 OR G2
85
LEGEND
DIGITAL TRANSMISSION FACILITY
PRIMARY FREQUENCY REFERENCE
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SECONDARY FREQUENCY REFERENCE
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.

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.
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DSO
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SYSTEM
DCO
75 OR 85
CEM
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SYSTEM
75
NOTE
SYNCHRONIZATION OF DIGITAL FACILITIES
DSO
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DCO
DACS
SYSTEM
D4
85
B-7
STRATUM 1
STRATUM 2
STRATUM 3
STRATUM 4