Synchronization Status Messaging - Cisco 15454-DS1-14= - 1.544Mbps Expansion Module Reference Manual

Chapter 10 Timing
Figure 10-1
Node 4
Timing Line
Ref 1: Slot 6
Ref 2: Slot 5
Ref 3: Internal (ST3)

10.3 Synchronization Status Messaging

Synchronization status messaging (SSM) is a SONET and SDH protocol that communicates information
about the quality of the timing source. SSM messages are transported as follows:
•
•
The SSM messages enable SONET and SDH devices to select the highest quality timing reference
automatically and to avoid timing loops.
78-18106-01
ONS 15454 Timing Example
Slot 6
Slot 5
If SSM is carried over an optical line, for both SONET and SDH the SSM is transported in the S1
byte.
If SSM is carried over an electrical line:
For SDH, the SSM is transported in the Sa bit of E1.
–
– For SONET, the SSM is transported in the outband loop code.
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 Reference Manual, R8.5
10.3 Synchronization Status Messaging
Node 2
Timing Line
Ref 1: Slot 5
Ref 2: Slot 6
Ref 3: Internal (ST3)
10-3