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Cisco ONS 15327 Troubleshooting Guide, R3.4
April 2003
Chapter 1 General Troubleshooting
Network Troubleshooting Tests
1.1 Network Troubleshooting Tests
Use loopbacks and hairpins to test newly created circuits before running live traffic or to logically locate
the source of a network failure. All ONS 15327 line (traffic) cards, except Ethernet cards, allow
loopbacks and hairpins.
Caution On OC-N cards, a facility loopback applies to the entire card and not an individual circuit. Exercise
caution when using loopbacks on an OC-N card carrying live traffic.
A facility loopback tests the line interface unit (LIU) of a card, the mechanical interface card (MIC), 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 MIC, or the cabling plant as the potential cause of a
network problem. Figure 1-1 shows a facility loopback on an XTC-14 or XTC-28-3 card.
Figure 1-1 Facility Loopback Process on an XTC Card
To test the LIU on an OC-N card, connect an optical test set to the OC-N port and perform a facility
loopback or use a loopback or hairpin on a card that is farther along the circuit path. Figure 1-2 shows a
facility loopback on an OC-N card.
Caution Before performing a facility loopback on an OC-N card, make 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, thus enabling you to remove the
facility loopback. Ensuring a second DCC is not necessary if you are directly connected to the
ONS 15327 containing the loopback OC-N card.
Figure 1-2 Facility Loopback Process on an OC-N Card
A terminal loopback tests a circuit path as it passes through the XTC card and loops back from the card
with the loopback. Figure 1-3 on page 1-3 shows a terminal loopback on an OC-N card. The test-set
traffic comes in on the MIC card DS-N ports and goes through the XTC card to the OC-N card. The
MIC OC-N
XTC
DS-N
DS-N
Facility
loopback
76186
Test Set A
OC-N OC-NXTC
90642
Test Set