Cisco Systems 15454 SDH 9.2 Node Timing

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Cisco ONS 15454 SDH Reference Manual, R5.0

April 2008

Chapter9 Security and Timin g

9.2 Node Timing

9.2 Node Timing

SDH timing parameters must be set for each ONS 15454 SDH. Each ONS 15454 SDH independently

accepts its timing reference from one of three sources:

•The building integrated timing supply (BITS) pins on the MIC-C/T/P coaxial connectors.

•An STM-N card installed in the ONS 15454 SDH. The card is connected to a node that receives

timing through a BITS source.

•The internal ST3 clock on the TCC2/TCC2P card.

You can set ONS15454 SDH timing to one of three modes: external, line, or mixed. If timing is coming

from the BITS pins, set the ONS15454 SDH timing to external. If the timing comes from an STM-N

card, set the timing to line. In typical ONS15454 SDH networks:

•One node is set to external. The external node derives its timing from a BITS source wired to the

BITS MIC-C/T/P coaxial connectors. The BITS source, 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 (span) cards. The MSTP normally derives timing from the line using the OSCM

or OSC-CSM card that are inside an STM-1 channel.

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

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

reference is usually assigned to the internal clock provided on every ONS 15454 SDH TCC2/TCC2P

card. However, if you assign all three references to other timing sources, the internal clock is always

available as a backup timing reference. The internal clock is a Stratum3 (ST3), so if an ONS 15454 SDH

node becomes isolated, timing is maintained at the ST3 level.

The CTC Maintenance > Timing > Report tabs show current timing infor mation for an ONS 15454 SDH,

including the timing mode, clock state and status, switch type, and reference data.

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.

Figure 9-1 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 wired to the BITS MIC-C/T/P

coaxial connectors on Node 1. The third reference is set to internal clock. The BITS outputs on Node 3

provide timing to outside equipment, such as a digital access line access multiplexer.

In the example, Slots 5 and 6 contain the trunk (span) card s. 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 1 is Slot 5 because it is

connected to Node 1. At Node 4, Reference 1 is set to Sl ot 6 because it is connected to Node 1. At

Node 3, Reference 1 could be either trunk card because they are an equal distance from Node 1.