Facility or terminal loopbacks can be service-affecting. To protect traffic, apply a lockout or Force switch to
the target loopback port. Basic directions for these procedures exist in
Alarm Troubleshooting, on page 99
chapter.
Caution
In CTC, a facility loopback is sometimes called facility (line) loopback, and a terminal loopback is sometimes
called a terminal (inward) loopback. This is done to indicate the terminating direction of the signal: a facility
loopback is sent outward toward the span, whereas a terminal loopback is redirected inward toward its
originating port.
Note
Facility Loopbacks
The following sections give general information about facility loopback operations and specific information
about card loopback activity.
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.
To test a card LIU, connect an optical test set to a trunk or client port and perform a facility loopback.
Alternately, use a loopback or hairpin circuit on a card that is farther along the circuit path. For example,
Figure 1: Facility Loopback Path on a Near-End Transponder Card, on page 3
shows a facility loopback at
a trunk port and at a client port on a TXP card.
Cisco NCS 2000 series Troubleshooting Guide, Release 11.0
2
General Troubleshooting
Facility Loopbacks
