Cisco Systems 15310-MA Manual

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

78-19417-01

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 6-1 shows 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

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.

Node 4

Timing Line

Ref 1: Slot 4

Ref 2: Slot 3

Ref 3: Internal (ST3)

Node 2

Timing Line

Ref 1: Slot 3

Ref 2: Slot 4

Ref 3: Internal (ST3)

Node 1

Timing External

Ref 1: BITS

Ref 2: Internal

Ref 3: Internal (ST3)

Node 3

Timing Line

Ref 1: Slot 3

Ref 2: Slot 4

Ref 3: Internal (ST3)

BITS

out

BITS

source

Third party

equipment

Slot 3

Slot 3

Slot 3

Slot 3

Slot 4

Slot 4

Slot 4

Slot 4

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