363-206-295
Transmission and Synchronization Interfaces
5-16
Issue 1
December 1997
Synchronization Messaging
5
SONET synchronization messaging is used to communicate the quality of
subnetwork timing, internal timing status, and timing states throughout a
subnetwork. Transitions to and from holdover or between OC-12 references, for
shelf timing, and to and from DS1 AIS, for the DS1 output, are based on
synchronization messages received over the OC-12 line from which the
DDM-2000 system is extracting timing. In ring networks with synchronization
messaging, either TG circuit pack allows line-timing and automatic switching from
either of the two ring optical interfaces.
The DDM-2000 Multiplexers provide a synchronization messaging feature to
ensure the integrity of network synchronization during both normal and abnormal
conditions. Through the use of synchronization messaging, the current quality of
the timing source can be conveyed from one DDM-2000 Multiplexer to the next.
This capability allows the DDM-2000 Multiplexers to automatically change their
timing reference in order to always maintain the highest quality timing available.
The capability also allows the DDM-2000 Multiplexers to inform a local BITS clock
when the DS1 timing output has been degraded and should no longer be used as
a reference. This synchronization messaging feature is based on the scheme
developed in the American National Standards Institute (ANSI) T1X1 standards
committee.
Applications
5
The applications that are currently supported with the synchronization messaging
feature can be divided into three categories:
1.
DS1 Timing Output Integrity
2.
Automatic Synchronization Reconfiguration
3.
Synchronization Provisioning Integrity.