Cisco Systems ONS 15600 Synchronization Status Messaging, Message Quality Description, Prs, Stu

Chapter 6 Timing

6.3 Synchronization Status Messaging

Figure 6-1 ONS 15600 Timing Example

BITS1 source

BITS2 source

Slot 11

Port 1

Node 1

Timing: External

Ref 1: BITS1

Ref 2: BITS2

Ref 3: Internal (STE)

Slot 12

Port 1

Node 4

Timing: Line

Ref 1: Slot 12, Port 1

Ref 2: Slot 11, Port 1

Ref 3: Internal (STE)

Slot 12	Slot 11	Node 2
Port 1	Port 1
		Timing: Line
		Ref 1: Slot 11, Port 1
		Ref 2: Slot 12, Port 1
		Ref 3: Internal (STE)
Slot 11	Slot 12
Port 1	Port 1
Slot 12	Slot 11
Port 1	Port 1

BITS1 BITS2

Out Out

Third party equipment

Node 3

Timing: Line

Ref 1: Slot 11, Port 1

Ref 2: Slot 12, Port 1

Ref 3: Internal (STE)

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6.3 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 set. Generation 2 is a newer version. If you enable SSM for the ONS 15600, consult your timing reference documentation to determine which message set to use. Table 6-1lists the Generation 1 message set.

Table 6-1 SSM Generation 1 Message Set

Message	Quality	Description
PRS	1	Primary reference source—Stratum 1
STU	2	Synchronization traceability unknown

Cisco ONS 15600 Reference Manual, R7.2

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