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Cisco ONS 15327 Troubleshooting Guide, R3.4
April 2003
Chapter 1 General Troubleshooting
Identify Points of Failure on a DS-N Circuit Path
A cross-connect loopback tests a circuit path as it passes through the cross-connect card and loops back
to the port being tested. Testing and verifying circuit integrity often involves taking down the whole line;
however, a cross-connect loopback allows you to create a loopback on any embedded channel at
supported payloads at the STS-1 granularity and higher. For example, you can loop back a single STS-1,
STS-3c, STS-6c, etc., on an optical facility without interrupting the other STS circuits.
You can create a cross-connect loopback on all working or protect optical ports unless the protect port
is used in a 1+1 protection group and is in working mode. If a terminal or facility loopback exists on a
port, you cannot use the cross-connect loopback. Figure 1-6 shows a cross-connect loopback on an
OC-N port.
Figure 1-6 Cross-Connect Loopback Process on an OC-N Port
1.2 Identify Points of Failure on a DS-N Circuit Path
Facility loopbacks, hairpin circuits, and terminal loopbacks are often used to test a circuit path through
the network or to logically isolate a fault. Performing a loopback test at each point along the circuit path
systematically isolates possible points of failure.
The example in this section tests an DS-N circuit on a two-node bidirectional line switched ring (BLSR).
Using a series of facility loopbacks, hairpin circuits, and terminal loopbacks, the path of the circuit is
traced and the possible points of failure are tested and eliminated. A logical progression of network test
procedures applies to this scenario:
1. Facility loopback on the source-node XTC port
2. Hairpin on the source-node XTC port
3. Terminal loopback to the destination-node XTC port
4. Hairpin on the destination-node XTC port
5. Facility loopback to the destination XTC port
Note The test sequence for your circuits differs according to the type of circuit and network topology.
Note All loopback tests require on-site personnel.
Note These procedures are performed when power connections to the node(s) or site(s) are assumed to be
within necessary specifications. If the network tests do not isolate the problems, troubleshoot outward
for power failure.
XTC
Test Set
OC-Ny
OC-Nx
x
90645