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Chapter 1
General Troubleshooting
1.1.1.1 General Behavior
A facility (line) loopback tests the line interface unit (LIU) of a card, the Front Mount Electrical
Connection (FMEC) card, 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 Front-Mount
Electrical Card (FMEC), or the cabling plant as the potential cause of a network problem.
shows a facility loopback on an E1-N-14 card.
Figure 1-1
Test Set
To test an optical card LIU, connect an optical test set to the optical port and perform a facility (line)
loopback. Or use a loopback or hairpin on a card that is farther along the circuit path.
a facility loopback on an STM-N card.
Figure 1-2
E3-12
In CTC, STM-N cards with facility loopbacks show an icon
on other cards in this release.
Figure 1-3
Before performing a facility (line) loopback on an optical card, be sure the card contains at least two data
Caution
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 SDH
containing the loopback optical card.
July 2005
Facility (Line) Loopback Path on a Near-End E1-N-14 Card
E3-12
XC
STM-N
Facility (Line) Loopback Process on a Near-End STM-N Card
XC
STM-N
Test Set
STM-N Facility Loopback Indicator
(Figure
1-3). Loopback icons are not shown
Cisco ONS 15454 SDH Troubleshooting Guide, R5.0
1.1.1 Facility Loopbacks
Figure 1-1
Figure 1-2
shows
1-3
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