Specifications

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Cisco ONS 15454 Installation and Operations Guide, R3.2
March 2002
Chapter 3 Node Setup
Setting Up ONS 15454 Timing
In the example, Slots 5 and 6 contain the trunk cards. Timing at Nodes 2, 3, and 4 is set to line, and the
timing references are set to the trunk cards based on distance from the BITS source. Reference 1 is set
to the trunk card closest to the BITS source. At Node 2, Reference 1is Slot 5 because it is connected to
Node 1. At Node 4, Reference 1 is set to Slot 6 because it is connected to Node 1. At Node 3, Reference
1 could be either trunk card because they are equal distance from Node 1.
Figure 3-8 An ONS 15454 timing example
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 15454,
consult your timing reference documentation to determine which message set to use. Table 3-4 and
Table 3-5 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