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Cisco ONS 15454 Installation and Operations Guide
November 2001
Chapter3 Node Setup
Setting Up ONS 15454 Timing
3.6.2 Synchronization Status Messaging
Synchronization Status Messaging (SSM) is a SONET protocol that communicates information about
the quality of the timing source. SSM messages are carried on the S1 byte of the SONET Line layer.
They enable SONET devices to automatically select the highest quality timing reference and to avoid
timing loops.
SSM messages are either Generation 1 or Generation 2. Generation 1 is the first and most widely
deployed SSM message set. Generation 2 is a newer version. If yo u ena ble SSM f or the ON S 1 5454,
consult your timing reference documentation to determine which message set to use. Ta ble 3-4 and
Table 3 -5 show the Generation 1 and Generation 2 message sets.

Procedure: Set up ONS 15454 Timing

Step 1 From the CTC node view, click the Provisioning > Timing tabs (Figure3-9).
Step 2 In the General Timing section, complete the following information:
Table3-4 SSM Generation 1 Message Set
Message Quality Description
PRS 1 Primary reference source – Stratum 1
STU 2 Sync traceability unknown
ST2 3 Stratum 2
ST3 4 Stratum 3
SMC 5 SONET minimum clock
ST4 6 Stratum 4
DUS 7 Do not use for timing synchronization
RES Reserved; quality level set by user
Table3-5 SSM Generation 2 Message Set
Message Quality Description
PRS 1 Primary reference source - Stratum 1
STU 2 Sync traceability unknown
ST2 3 Stratum 2
TNC 4 Transit node clock
ST3E 5 Str atum 3 E
ST3 6 Stratum 3
SMC 7 SONET minimum clock
ST4 8 Stratum 4
DUS 9 Do not use for timing synchronization
RES Reserved; quality level set by user