1-4
Cisco ONS 15327 Troubleshooting Guide, R3.4
April 2003
Chapter1 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 car d 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 embedd ed cha nne l a t
supported payloads at the STS-1 granularity and higher. For example, you can loop back a si ngle 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 un less the pr ote ct p ort
is used in a 1+1 protection group and is in working mode . If a t erm i nal or faci lity l oop back exi sts on a
port, you cannot use the cross-connect loopback. Figure 1-6 shows a cross-connect loopbac k on an
OC-N port.
Figure1-6 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 oft en used to test a circuit path through
the network or to logically isolate a fault. Performing a loopback test at each po int 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 circui t 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 t he t y pe of c irc uit a nd net work t op ology.
Note All loopback tests require on-site personnel.
Note These procedures are performed when power connections to the node(s) or site(s) are assu med 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