3-12
Cisco ONS 15327 User Documentation, R3.3
June 2002
Chapter 3 Node Setup
Setting Up ONS 15327 Timing
Figure 3-4
An ONS 15327 timing example with external, BITS, and internal 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 you enable SSM for the ONS 15327,
consult your timing reference documentation to determine which message set to use.
and
show the Generation 1 and Generation 2 message sets.
Node 4
Timing Line
Ref 1: Slot 4
Ref 2: Slot 3
Ref 3: Internal (ST3)
Node 2
Timing Line
Ref 1: Slot 3
Ref 2: Slot 4
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 3
Ref 2: Slot 4
Ref 3: Internal (ST3)
BITS1
out
BITS2
out
BITS1
source
BITS2
source
Third party
equipment
Slot 3
Slot 3
Slot 3
Slot 3
Slot 4
Slot 4
Slot 4
Slot 4
78234
Table 3-4
SSM Generation 1 Message Set
Message
Quality
Description
PRS
1
Primary reference source – Stratum 1
STU
2
Sync traceability unknown
ST2
3
Stratum 2
Summary of Contents for ONS 15327
Page 22: ...Contents xxii Cisco ONS 15327 User Documentation June 2002 I N D E X ...
Page 30: ...Figures xxviii Cisco ONS 15327 User Documentation June 2002 ...
Page 44: ...Procedures xlii Cisco ONS 15454 Installation and Operations Guide R3 2 June 2002 ...
Page 540: ...Glossary GL 16 Cisco ONS 15327 User Documentation R3 3 June 2002 ...