363-206-305
Transmission and Synchronization
5-16
Issue 3 June 2000
interface, and all other OC-N interfaces that are enabled for synchronization
messaging, the appropriate message indicating the quality of its timing and its
active timing mode. Table 5-1 lists the associated internal timing status that is
associated with synchronization messages received from the OC-N interface
when synchronization messaging is enabled. The table lists the messages from
low to high quality.
The "Don't Use" message is sent when the system determines that its timing is
not suitable for synchronization, for example, due to failure.
When the DDM-2000 FiberReach system is in holdover mode, the Internal Clock
message will be sent on all OC-N interfaces.
When the DDM-2000 FiberReach system is configured for line timing, the Timing
Looped Back message will be sent on the OC-N interfaces toward the network
element 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 enabled.
With automatic synchronization reconfiguration, the DDM-2000 FiberReach
Multiplexer systems use and compare the incoming synchronization messages on
the OC-1 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 5-1. Synchronization Messages Using K2 Byte
Received Message Active Timing Mode
Don't Use Holdover
Timing Looped Back (TLB) Holdover
Stratum 4
*
* Presently, DDM Multiplexers cannot generate these messages, but
they could be transmitted and supported for auto-reconfiguration if any
of these are received by DDM-2000 Multiplexer.
Holdover
Internal Clock (IC) OK to use
Stratum 3* OK to use
Stratum 2* OK to use
Sync Quality Unknown
(SQU)
OK to use
Stratum 1* OK to use
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