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Cisco ONS 15600 Reference Manual, R7.2
Chapter 6 Timing
6.3 Synchronization Status Messaging
Figure 6-1 ONS 15600 Timing Example
6.3 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 set. Generation 2 is a newer version. If you enable SSM for the ONS 15600, consult your
timing reference documentation to determine which message set to use. Table 6-1 lists the Generation 1
message set.
Node 4
Timing: Line
Ref 1: Slot 12, Port 1
Ref 2: Slot 11, Port 1
Ref 3: Internal (STE)
Node 2
Timing: Line
Ref 1: Slot 11, Port 1
Ref 2: Slot 12, Port 1
Ref 3: Internal (STE)
Node 1
Timing: External
Ref 1: BITS1
Ref 2: BITS2
Ref 3: Internal (STE)
Node 3
Timing: Line
Ref 1: Slot 11, Port 1
Ref 2: Slot 12, Port 1
Ref 3: Internal (STE)
BITS1
source
BITS2
source
120368
Slot 11
Port 1
Slot 11
Port 1
Slot 11
Port 1
Slot 11
Port 1
Slot 12
Port 1
Slot 12
Port 1
Slot 12
Port 1
Slot 12
Port 1
BITS1
Out
BITS2
Out
Third party
equipment
Table 6-1 SSM Generation 1 Message Set
Message Quality Description
PRS 1 Primary reference source—Stratum 1
STU 2 Synchronization traceability unknown