363-206-295
Transmission and Synchronization Interfaces
Issue 1
December 1997
5-23
message SQU for K byte, or STU for S byte, will be transmitted on all OC-N
interfaces.
When the DDM-2000 OC-12 system is configured for free-run or is in holdover
mode, the Internal Clock message for K byte, or Traceable SONET minimum Clk
for S byte, will be sent on all OC-N interfaces where synchronization messaging is
provisioned.
When the DDM-2000 OC-12 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 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 takes precedence. This
feature guarantees the nonrevertive operation of reconfiguration. The line-timing
reference is provisioned by the
set-sync
command. Table 5-3 lists the
synchronization messages in ascending order.
The existence of automatic synchronization reconfiguration does not change the
system's behavior on traditional line failures; for example, loss of frame (LOF),
loss of signal (LOS), and others.
There are synchronization references in the DDM-2000 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 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.
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
