Cisco ONS 15454 DWDM - Page 561

14-3
Cisco ONS 15454 DWDM Reference Manual, R8.5
78-18343-02
Chapter 14 Timing Reference
14.3 Synchronization Status Messaging
Figure 14-1 ONS 15454 Timing Example
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 14-1 and
Table 14-2 on page 14-4 show the Generation 1 and Generation 2 message sets.
Node 4
Timing Line
Ref 1: Slot 6
Ref 2: Slot 5
Ref 3: Internal (ST3)
Node 2
Timing Line
Ref 1: Slot 5
Ref 2: Slot 6
Ref 3: Internal (ST3)
Node 1
Timing External
Ref 1: BITS1
Ref 2: BITS2
Ref 3: Internal (ST3)
Node 3
Timing Line
Ref 1: Slot 5
Ref 2: Slot 6
Ref 3: Internal (ST3)
BITS1
out
BITS2
out
BITS1
source
BITS2
source
Third party
equipment
34726
Slot 5
Slot 5
Slot 5
Slot 5
Slot 6
Slot 6
Slot 6
Slot 6
Table 14-1 SSM Generation 1 Message Set
Message Quality Description
PRS 1 Primary reference source—Stratum 1
STU 2 Synchronization traceability unknown