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Cisco ONS 15327 Troubleshooting Guide, R3.4
April 2003
Chapter 1 General Troubleshooting
Network Troubleshooting Tests
terminal loopback on the OC-N card turns the signal around before it reaches the LIU and sends it back
through the XTC card to the MIC card. This test verifies that the XTC card cross-connect circuit paths
are valid, but does not test the LIU on the OC-N card.
Figure 1-3 Terminal Loopback Process on an OC-N Card
Figure 1-4 shows a terminal loopback on a G1000-2 card. The test-set traffic comes in on the MIC card
DS-N ports and goes through the XTC card to the G1000-2 card. The terminal loopback on the
G1000-2 card turns the signal around before it reaches the LIU and sends it back through the XTC card
to the MIC card. This test verifies that the XTC card cross-connect circuit paths are valid, but does not
test the LIU on the G1000-2 card.
Figure 1-4 Terminal Loopback Process on a G1000-2 Card
A hairpin circuit brings traffic in and out on a DS-N port instead of sending the traffic onto the OC-N.
A hairpin loops back only the specific STS or VT circuit and does not cause an entire OC-N port to loop
back, which would drop all traffic on the OC-N port. The hairpin allows you to test a circuit on nodes
running live traffic. Figure 1-5 shows the hairpin circuit process on a OC-N card.
Figure 1-5 Hairpin Circuit Process on an OC-N Card
DS-N
MIC OC-N
DS-N
Test Set A
Terminal loopback
XTC
76191
MIC
G1000-2
XTC
90641
Test Set
DS-N
MIC OC-N
DS-N
Test Set A
76193
Hairpin circuit
XTC