Cisco ONS 15454 DWDM Reference Manual page 561

Chapter 14 Timing Reference
Figure 14-1
Node 4
Timing Line
Ref 1: Slot 6
Ref 2: Slot 5
Ref 3: Internal (ST3)
14.3 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 message set. Generation 2 is a newer version. If you enable SSM for the ONS 15454,
consult your timing reference documentation to determine which message set to use.
Table 14-2 on page 14-4
Table 14-1
Message
PRS
STU
78-18343-02
ONS 15454 Timing Example
Slot 6
Slot 5
show the Generation 1 and Generation 2 message sets.
SSM Generation 1 Message Set
Quality Description
1 Primary reference source—Stratum 1
2 Synchronization traceability unknown
BITS1 BITS2
source source
Node 1
Timing External
Ref 1: BITS1
Ref 2: BITS2
Ref 3: Internal (ST3)
Slot 5 Slot 6
Slot 5
Slot 6
Slot 6
Slot 5
Node 3
Timing Line
Ref 1: Slot 5
BITS1 BITS2
out out Ref 2: Slot 6
Ref 3: Internal (ST3)
Third party
equipment
Cisco ONS 15454 DWDM Reference Manual, R8.5
14.3 Synchronization Status Messaging
Node 2
Timing Line
Ref 1: Slot 5
Ref 2: Slot 6
Ref 3: Internal (ST3)
Table 14-1 and
14-3