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SYNC (Synchronization)
Issue 4 May 2002 10-1587 555-233-123
Figure 10-91. Typical Stratum 4 Synchronization Configuration
If the primary synchronization reference in the previous diagram is providing a
valid timing signal, then the flow of system synchronization would travel from the
DS1 interface circuit pack in the PPN across the active Expansion Interface fiber
link to the two EPNs. The PPNDS1 interface circuit pack provides a timing signal
for the PPN Tone-Clock circuit pack and the PPN Tone-Clock circuit pack provides
timing for all circuit packs in the PPN. The PPN Expansion Interface circuit pack
uses the timing generated by the Tone-Clock circuit pack to generate a data
stream which is sent across the Expansion Interface link to the Expansion
Interface circuit packs in the two EPNs. The EPN Expansion Interface circuit pack
uses the received data stream to generate a timing signal. The Tone-Clock circuit
pack in the EPNs uses this signal to generate timing for all the circuit packs in
their respective EPNs. The PPN, in the above mentioned scenario, is designated
the master port network and the EPNs are called slave port networks. The master
port network is defined as the port network that contains the system
synchronization source. If the primary synchronization reference does not provide
a valid timing signal, Synchronization Maintenance switches to the secondary
reference. Both the primary and secondary references must reside in the
PPN
EPN EPN
TONE/
CLOCK
DS-1
INTF
DS-1
INTF
PRIMARY
REFERENCE
SECONDARY
REFERENCE
TIMING
INFO
EXPANSION INTERFACE (EI) LINK*
* EPN-TO-EPN LINKS ARE NOT USED TO CARRY TIMING
TIMING
INFO
EI LINK EI LINK