363-206-285
Transmission and Synchronization Interfaces
Issue 3 June 2001
5-41
generating AIS while the system is configured in this way, the message SQU for K
byte, or STU for S byte, will be transmitted on all OC-N interfaces.
When the DDM-2000 OC-3 system is configured for free run or is in holdover
mode, the Internal Clock message for K byte or Traceable SONET Clk for S byte
will be sent on all OC-N interfaces where synchronization messaging is
provisioned.
When the DDM-2000 OC-3 system is configured for line timing, the TLB message
for K byte and “Don’t Use” for S byte will be sent on the OC-N interfaces towards
the NE from which the timing is being derived. The message received on the
OC-N interface will be sent on all other OC-N interfaces where synchronization
messaging is provisioned.
With automatic synchronization reconfiguration, the DDM-2000 OC-3 Multiplexer
systems use and compare the incoming synchronization messages on the OC-N
interfaces available for line timing to select the highest quality synchronization
reference available. If the received quality levels are the same on the references
available for timing, the existing line timing reference take precedence. This
feature guarantees the non-revertive operation of reconfiguration. The line timing
reference is provisioned by the set-sync command.
The existence of automatic synchronization reconfiguration does not change the
system's behavior on traditional line failures; for example, LOF, LOP, LOS, and
others.
There are synchronization references in the DDM-2000 OC-3 system that can be
provisioned as network timing sources but are not considered as timing sources
for automatic synchronization reconfiguration. Examples of these are the linear
extensions off of a DDM-2000 OC-3 ring. This type of interface is considered a
linear interface, and the system treats it as such with regards to synchronization.
Table 5-5 lists the synchronization references available on DDM-2000 OC-3 and
OC-12 system topologies.
Function unit C, when equipped with an OC-3/IS-3 OLIU, can be selected as an
option for automatic synchronization reconfiguration. This is useful in DRI
networks where an OC-3 ring is connected through an OC-3/IS-3 optical interface
to an OC-12 or FT-2000 OC-48 Lightwave System ring.
Table 5-5. Available Synchronization References
System Manually Provisionable Automatically Reconfigurable
OC-3 Linear Main, Fn-C Main, Fn-C
OC-3 Rings Main-1, Main-2, Fn-C Main-1, Main-2, Fn-C
OC-12 Linear Main-B Not applicable
OC-12 Rings Main-B-1, Main-B-2 Main-B-1, Main-B-2
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