Synchronization Status Messaging; Figure 3-4 An Ons 15327 Timing Example With External, Bits, And Internal Timing; Table 3-4 Ssm Generation 1 Message Set - Cisco ONS 15327 User Documentation

Setting Up ONS 15327 Timing
Figure 3-4
Node 4
Timing Line
Ref 1: Slot 4
Ref 2: Slot 3
Ref 3: Internal (ST3)

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.
Table 3-5
Table 3-4
Message
PRS
STU
ST2
Cisco ONS 15327 User Documentation, R3.3
3-12
An ONS 15327 timing example with external, BITS, and internal timing
Slot 4
Slot 3
show the Generation 1 and Generation 2 message sets.
SSM Generation 1 Message Set
Quality Description
1 Primary reference source – Stratum 1
2 Sync traceability unknown
3 Stratum 2
BITS1 BITS2
source source
Node 1
Timing External
Ref 1: BITS1
Ref 2: BITS2
Ref 3: Internal (ST3)
Slot 3 Slot 4
Slot 3
Slot 4
Slot 4
Slot 3
Node 3
Timing Line
BITS1 BITS2 Ref 1: Slot 3
Ref 2: Slot 4
out out
Ref 3: Internal (ST3)
Third party
equipment
Chapter 3 Node Setup
Node 2
Timing Line
Ref 1: Slot 3
Ref 2: Slot 4
Ref 3: Internal (ST3)
Table 3-4 and
June 2002