Figure 12-10 The Facility Loopback Process On An Xtc Card; Figure 12-11 The Hairpin Circuit Process On An Oc-N Card - Cisco ONS 15327 User Documentation

Network Tests
Before performing a facility loopback on an OC-N card, make sure there is another SDCC path to the
Caution
ONS 15327 containing the OC-N card being put in loopback. A second SDCC path is necessary to
provide a non-looped path to log into the ONS 15327 containing the OC-N card being put in loopback
to enable removal of the facility loopback. This is not necessary if you are directly connected to the
ONS 15327 containing the OC-N card being put in facility loopback.

Figure 12-10 The facility loopback process on an XTC card

Test Set A
Facility
loopback
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 12-11 The hairpin circuit process on an OC-N card

Test Set A
A terminal loopback tests a circuit path through the XTC card and as it loops back from the line card
being tested.
on the MIC card DS-N ports and goes through the XTC card to the OC-N card. The terminal loopback
on the OC-N card turns the signal around before it reaches the line interface and sends it through the
XTC card to the MIC card. This test verifies that the XTC cross-connect circuit paths are valid, but does
not test the line interface on the OC-N card. To test the line interface on an OC-N card, connect an optical
test set to the OC-N card ports and perform a facility loopback or use a loopback or hairpin on a card
that is farther along the circuit path.
Cisco ONS 15327 User Documentation, R3.3
12-20
XTC
MIC OC-N
DS-N
DS-N
XTC
DS-N
MIC OC-N
DS-N
Figure 12-12 shows a terminal loopback set on an OC-N card. The test-set traffic comes in
Hairpin circuit
Chapter 12 Maintenance
June 2002