Setting Up Ons 15327 Timing; Network Timing Example - Cisco ONS 15327 User Documentation

Chapter 3 Node Setup

3.6 Setting Up ONS 15327 Timing

SONET timing parameters must be set for each ONS 15327. Each ONS 15327 independently accepts its
timing reference from one of three sources:
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•
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You can set ONS 15327 timing to one of three modes: external, line, or mixed. If timing is coming from
the BITS port, set ONS 15327 timing to external. If the timing comes from an OC-N card, set the timing
to line. In typical ONS 15327 networks:
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You can set three timing references for each ONS 15327. The first two references are typically two
BITS-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 15327 XTC card. This clock is a Stratum 3 (ST3).
If an ONS 15327 becomes isolated, timing is maintained at the ST3 level.
Mixed timing allows you to select both external and line timing sources. However, Cisco does not
Caution
recommend its use because it can create timing loops. Use this mode with caution.

3.6.1 Network Timing Example

Figure 3-4
Two references are set to BITS, and the third reference is set to internal. The BITS output pins on the
MICs of Node 3 provide timing to outside equipment, such as a Digital Access Line Access Multiplexer.
June 2002
An OC-N card installed in the ONS 15327. The card is connected to a node that receives timing
through a BITS source.
The internal ST3 clock on the XTC card
A BITS source connected to the BITS port on the MIC
One node is set to external. The external node derives its timing from a BITS source wired to the
BITS port. The BITS source, in turn, derives its timing from a Primary Reference Source (PRS) such
as a Stratum 1 clock or GPS signal.
The other nodes are set to line. The line nodes derive timing from the externally-timed node through
the OC-N trunk cards.
shows an example of an ONS 15327 network timing setup. Node 1 is set to external timing.
Setting Up ONS 15327 Timing
Cisco ONS 15327 User Documentation, R3.3
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