Cisco ONS 15454 SDH - Optical Multiplex Section Layer; Optical Transmission Section Layer; Performance Monitoring Counters and Threshold Crossing Alerts

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Cisco ONS 15454 SDH Troubleshooting Guide, R5.0
July 2005
Chapter 1 General Troubleshooting
1.6.3 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.
1.6.3 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 32-Channel Multiplexer—Odd Channels (32MUX-O) and a demultiplexer such
as the 32-Channel Demultiplexer—Odd Channels (32 DMX-O).
1.6.4 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 and an amplifier such as the OPT-PRE
• An amplifier and another amplifier, such as the OPT-BST and the OPT-PRE
• An amplifier such as the OPT-BST and a demultiplexer such as the 32-DMX
1.6.5 Performance Monitoring Counters and Threshold Crossing Alerts
Performance monitoring (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 which 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 performance monitoring count parameters are associated with different read points in a
network. Figure 1-41 illustrates the performance monitoring read points that are useful in identifying
DWDM circuit points of failure. Chapter 4, “Performance Monitoring,” 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 performance monitoring parameters are
associated with the system points you want to monitor or provision with CTC or TL1. The monitoring
points can vary according to your configuration.