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Cisco ONS 15454 SDH Troubleshooting Guide, R5.0
July 2005
Chapter 1 General Troubleshooting
1.4 Troubleshooting Ethernet Circuit Paths With Loopbacks
The entire circuit path has now passed its comprehensive series of loopback tests. This circuit qualifies
to carry live traffic.
1.4 Troubleshooting Ethernet Circuit Paths With Loopbacks
Terminal loopbacks, hairpin circuits, and terminal loopbacks can be used in the order shown in this
section to troubleshoot an Ethernet circuit path for the G-Series card. E-Series and ML-Series do not
have this capability in Software Release 5.0. The example in this section tests a G1000 circuit on a
three-node MS-SPRing. Using a series of facility (line) loopbacks and terminal (inward) loopbacks, the
example scenario traces the circuit path, tests the possible failure points, and eliminates them. The
logical progression contains six network test procedures:
Note The test sequence for your circuits will differ according to the type of circuit and network topology.
1. A facility (line) loopback on the source-node Ethernet port
2. A terminal (inward) loopback on the source-node Ethernet port
3. A facility (line) loopback on the intermediate-node Ethernet port
4. A terminal (inward) loopback on the intermediate-node Ethernet port
5. A facility (line) loopback on the destination-node Ethernet port
6. A terminal (inward) loopback on the destination-node Ethernet port
Note Facility and terminal loopback tests require on-site personnel.
1.4.1 Perform a Facility (Line) Loopback on a Source-Node Ethernet Port
The facility (line) loopback test is performed on the node source port in the network circuit. In the testing
situation used in this example, the source G1000 port in the source node. Completing a successful
facility (line) loopback on this port isolates the G1000 port as a possible failure point. Figure 1-28 shows
an example of a facility loopback on a circuit source Ethernet port.
Figure 1-28 Facility (Line) Loopback on a Circuit Source Ethernet Port
Caution Performing a loopback on an in-service circuit is service-affecting.
Destination
ONS Node
XC
Source
ONS Node
Intermediate
ONS Node
Test Set
Ethernet EthernetEthernet Ethernet Ethernet Ethernet
XCXC
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