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Cisco ONS 15454 DWDM Troubleshooting Guide, R7.0.1
78-17742-02
Chapter 1 General Troubleshooting
1.3.3 Optical Multiplex Section Layer
2. A second overhead is added to the OPUk unit to create the optical channel data unit (ODUk).
3. A third overhead including forward error correction (FEC) is added to the ODUk to create the
optical channel transport unit (OTUk).
4. A fourth overhead is added to the OTUk to create the entire OCH layer.
1.3.3 Optical Multiplex Section Layer
The optical multiplex section (OMS) of the OTN allows carriers to identify errors occurring within
DWDM network sections. The OMS layer consists of a payload and an overhead (OMS-OH). It supports
the ability to monitor multiplexed sections of the network, for example, the span between an optical
multiplexer such as the 32MUX-O card and an optical demultiplexer such as the 32DMX-O card.
1.3.4 Optical Transmission Section Layer
The optical transmission section (OTS) layer supports monitoring partial spans of a network’s
multiplexed sections. This layer consists of a payload and an overhead (OTS-OH). It is a transmission
span between two elements in an optical network, such as between:
• A multiplexer such as the 32MUX-O card and an amplifier such as the OPT-PRE card
• An amplifier and another amplifier, such as the OPT-BST card and the OPT-PRE card
• An amplifier such as the OPT-BST card and a demultiplexer such as the 32DMX card
1.3.5 Performance Monitoring Counters and Threshold Crossing Alerts
PM counters and TCAs can be used for identifying trouble and troubleshooting problems in
ITU-T G.709 optical transport networks. ITU-T Recommendation M.2401 recommends that the
following PM parameters be monitored at the ODUk layer:
• SES (severely errored seconds)—A one-second period that contains greater than or equal to
30 percent errored blocks or at least one defect. SES is a subset of the errored second (ES)
parameter, which is a one-second period with one or more errored blocks or at least one defect.
• BBE (background block error counter)—An errored block not occurring as part of an SES. BBE is
a subset of the errored block (EB) parameter, which is a block in which one or more bits are in error.
Different PM count parameters are associated with different read points in a network. Figure 1-10
illustrates the PM read points that are useful in identifying DWDM circuit points of failure. The
“Performance Monitoring” chapter in the Cisco ONS 15454 DWDM Reference Manual lists all PM
parameters and provides block diagrams of signal entry points, exit points, and interconnections between
the individual circuit cards. Consult these specifications to determine which PM parameters are
associated with the system points you want to monitor or provision with CTC or TL1. The monitoring
points might vary according to your configuration.
Note When LOS, LOS-P, or LOF alarms occur on TXP and MXP trunks, G709/SONET/SDH TCAs are
suppressed. For details, see the “Alarm and TCA Monitoring and Management” chapter in the
Cisco ONS 15454 DWDM Reference Manual.
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