AT&T Telephone DS1/DMi/ISDN-PRI Manuale Utente Scaricare il pdf (Pagina 97)

100

101

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.

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AT&T Telephone DS1/DMi/ISDN-PRI Manuale Utente Pagina 97

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