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System Management
Synchronization Status Messages (SSM)
Synchronization Status Messaging (SSM) provides a mechanism for downstream network
elements to determine the traceability of the synchronization trail back to the highest quality clock
available. Synchronization Status messages have been defined for various transport protocols and
are placed in prescribed overhead bytes for SONET and SDH signals and also in bit-oriented
messages within the (ESF) data link for DS1 and E1 signals, for interaction with office clocks,
such as BITS or SSUs.
The following section elaborates on the messages as they are applied to Synchronous Ethernet and
messaging within a packet transport network.
Synchronization Status Messaging enables signaling of stratum level, notification of failures, and
taking of appropriate actions. SSM is used for selecting the best timing source by communicating
the quality of the network timing throughout the network. A standardized message set defined in
ITU-T G.707 and G.781. A number of quality levels several user assignable are available to
convey to a downstream clock information such as Stratum level (for example., 1, 2, 3, SMC, or 4)
Traceable, Synchronized - Traceability Unknown (STU), and DON'T USE for Synchronization
(DUS). A summary of some of the details are shown in
Figure
14.
Figure 14: Synchronization Status Messages
7710 SR OS Basic System Configuration Guide
Page 199
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