Facility Loopbacks - Cisco NCS 2000 series Troubleshooting Manual

Facility Loopbacks

Caution
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
chapter.
Note 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.
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
a trunk port and at a client port on a TXP card.
Cisco NCS 2000 series Troubleshooting Guide, Release 11.0
2
General Troubleshooting
Alarm Troubleshooting, on page 99
shows a facility loopback at