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Cisco ONS 15327 Troubleshooting Guide, R3.4
April 2003
Chapter1 General Troubleshooting
Network Troubleshooting Tests
1.1 Network Troubleshooting Tests
Use loopbacks and hairpins to test newly created circuits before running live traf f ic or to logic ally locate
the source of a network failure. All ONS15327 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 carryin g l ive 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 po tential cause of a
network problem. Figure 1-1 shows a facility loopback on an XTC-14 or XTC-28-3 card.
Figure1-1 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 alon g 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 c a rd, m ake sur e the c ard co ntai n s at le ast two da ta
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.
Figure1-2 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 pag e 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