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Cisco ONS 15454 Troubleshooting Guide, R8.5
November 2009
Chapter 1 General Troubleshooting
1.1.1 Facility Loopbacks
1.1.1 Facility Loopbacks
The following sections give general information about facility loopback operations and specific
information about ONS 15454 card loopback activity.
1.1.1.1 General Behavior
A facility loopback tests the line interface unit (LIU) of a card, the electrical interface assembly (EIA),
and related cabling. After applying a facility loopback on a port, use a test set to run traffic over the
loopback. A successful facility loopback isolates the LIU, the EIA, or the cabling plant as the potential
cause of a network problem. Figure 1-1 shows a facility loopback on a DS-N electrical card.
Figure 1-1 Facility Loopback Path on a Near-End DS-N Card
To test an OC-N card LIU, connect an optical test set to the OC-N port and perform a facility loopback.
Alternately, use a loopback or hairpin circuit on a card that is farther along the circuit path. Figure 1-2
shows a facility loopback on an OC-N card.
Figure 1-2 Facility Loopback Path on a Near-End OC-N Card
In CTC, OC-N cards with facility loopbacks show an icon (Figure 1-3). Loopback icons are not shown
on other cards in this release.
Figure 1-3 OC-N Facility Loopback Indicator
Caution Before performing a facility loopback on an OC-N card, be sure the card contains at least two data
communications channel (DCC) paths to the node where the card is installed. A second DCC provides
a nonlooped path to log into the node after the loopback is applied, enabling you to remove the facility
loopback. Ensuring a second DCC is not necessary if you are directly connected to the ONS 15454
containing the loopback OC-N card.
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