Cisco ONS 15454 Troubleshooting Manual page 155

Chapter 1 General Troubleshooting
The diagnostic circuit is bidirectional and uses a single VT 1.5 in an STS. The circuit can traverse
multiple nodes, but it must be carried by the same STS for the entire path. The circuit originates and
ultimately destinates on the same node, but can be looped (by a hairpin circuit) through other nodes.
After the circuit returns to the originating node, the signal result is detected and analyzed for errors by
PRBS.
This type of circuit is created much the same way as a normal standby protection channel access (PCA)
circuit, but is designated by checking the Diagnostic check box during circuit creation. A normal circuit
uses line cards as the endpoints, but if a circuit is configured as a diagnostic, the endpoints are
cross-connect cards.
Each card type utilizes the diagnostic feature differently. Standby electrical cards run PRBS tests to
ensure signal path integrity. Optical cards do not run PRBS tests, but instead run ASIC tests to test card
operability. Cross-connect cards verify the standby paths.
The diagnostic circuit can be configured for an end-to-end or multiple-node path layout, traversing the
transmit and receive standby paths as shown in
Figure 1-45
Detector
Node A
The maximum diagnostic circuit size is VT1.5, and the maximum quantity of available diagnostic
circuits is one per node. (In other words, if you create a diagnostic VT within an STS, the remaining 27
VTs can still be provisioned, and they may also contain diagnostic circuits originating on other nodes.)
As with all bidirectional circuits, a diagnostic circuit can only be created if the same STS is available on
each span the circuit traverses. When you use a bidirectional diagnostic that traverses one or more
intermediate nodes, create or utilize an existing bidirectional circuit on each intermediate node. At the
terminating node, you will need to create a hairpin loopback at the end of the PRBS source span to return
the signal.
November 2009
CTC Node View Diagnostic Window
PRBS PRBS
Generator
VT PRBS signal that tests all spans on the BLSR ring.
VT PRBS signal that tests only one span on the BLSR ring.
NOTE: The end without the arrow is where the PRBS pattern is generated.
The end with the arrow is the end where the PRBS pattern is detected.
Figure 1-45.
Node C
Node B
Node H
Node G
Cisco ONS 15454 Troubleshooting Guide, R8.5
1.7.3 Bidirectional Diagnostic Circuit
Node D
Node E
Node F
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