Cisco Systems 15310-MA manual Network Timing, Synchronization Status Messaging

Chapter 6 Timing

Network Timing

Caution Mixed timing allows you to select both external and line timing sources. However, Cisco does not recommend its use because it can create timing loops. Use mixed timing mode with caution.

6.2 Network Timing

Figure 6-1shows an example of an ONS 15310-MA SDH network timing setup. Node 1 is set to external timing. One reference is set to BITS, the two references are set to internal. The BITS output pins on the CTX cards of Node 3 provide timing to outside equipment, such as a digital access line multiplexer.

Figure 6-1 ONS 15310-MA SDH Timing Example

BITS

source

Node 1

Timing External

Ref 1: BITS

Ref 2: Internal

Ref 3: Internal (ST3)

Slot 3 Slot 4

Node 4	Slot 4	Slot 3	Node 2
Timing Line			Timing Line
Ref 1: Slot 4			Ref 1: Slot 3
Ref 2: Slot 3			Ref 2: Slot 4
Ref 3: Internal (ST3)			Ref 3: Internal (ST3)
	Slot 3	Slot 4

Slot 4 Slot 3

BITS

out

Third party equipment

Node 3

Timing Line

Ref 1: Slot 3

Ref 2: Slot 4

Ref 3: Internal (ST3)

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6.3 Synchronization Status Messaging

Synchronization status messaging (SSM) is an SDH protocol that communicates information about the quality of the timing source. SSM messages are carried on the S1 byte of the SDH line layer. They enable SDH devices to automatically select the highest quality timing reference and to avoid timing loops.

Cisco ONS 15310-MA SDH Reference Manual, Release 9.1 and Release 9.2

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