Cisco ONS 15454 SDH Specifications download pdf (Page 157)

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Cisco ONS 15454 SDH Installation and Operations Guide, R3.3

May 2002

Chapter 3 Node Setup

Setting Up ONS 15454 SDH Timing

In typical ONS 15454 SDH networks:

• One node is set to external. The external node derives its timing from a MIC-C/T/P FMEC timing

connector. The MIC-C/T/P FMEC, in turn, derives its timing from a Primary Reference Source

(PRS) such as a Stratum 1 clock or global positioning satellite (GPS) signal.

• The other nodes are set to line. The line nodes derive timing from the externally-timed node through

the STM-N trunk cards.

You can set three timing references for each ONS 15454 SDH. The first two references are typically two

FMEC-level sources, or two line-level sources optically connected to a node with a BITS source. The

third reference is the internal clock provided on every ONS 15454 SDH TCC-I card. This clock is a

Stratum 3 (ST3). If an ONS 15454 SDH becomes isolated, timing is maintained at the ST3 level.

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 this mode with caution.

3.5.2 Network Timing Example

Figure 3-13 shows an ONS 15454 SDH network timing setup example. Node 1 is set to external timing.

Two timing references are set to BITS. These are Stratum 1 timing sources connected to the MIC-C/T/P

FMEC. The third reference is set to internal clock. The Timing A and Timing B out connectors on the

MIC-C/T/P FMEC of Node 3 are used to provide timing to outside equipment.

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 MIC-C/T/P FMEC. Reference 1

is set to the trunk card closest to the timing source. At Node 2, Reference 1 is 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.

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