Synchronization Status Messaging; Figure 6-1 Ons 15600 Sdh Timing Example - Cisco ONS 15600 Reference Manual

Chapter 6 Timing
Figure 6-1
Node 4
Timing: Line
Ref 1: Slot 12, Port 1
Ref 2: Slot 11, Port 1
Ref 3: Internal (STE)

6.3 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.
78-18400-01
ONS 15600 SDH Timing Example
Slot 12
Slot 11
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
Slot 11 Slot 12
Port 1 Port 1
Port 1
Port 1
Slot 12 Slot 11
Port 1 Port 1
BITS1 BITS2
Out Out
Third party
equipment
Cisco ONS 15600 SDH Reference Manual, Release 9.0
6.3 Synchronization Status Messaging
Node 1
Timing: External
Ref 1: BITS1
Ref 2: BITS2
Ref 3: Internal (STE)
Slot 11
Node 2
Port 1
Timing: Line
Ref 1: Slot 11, Port 1
Ref 2: Slot 12, Port 1
Ref 3: Internal (STE)
Slot 12
Port 1
Node 3
Timing: Line
Ref 1: Slot 11, Port 1
Ref 2: Slot 12, Port 1
Ref 3: Internal (STE)
6-3