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Cisco ONS 15454 SDH Troubleshooting Guide, R5.0
July 2005
Chapter 1 General Troubleshooting
1.1.2 Terminal Loopbacks
1.1.2 Terminal Loopbacks
The following sections give general information about terminal loopback operations and specific
information about ONS 15454 SDH card loopback activity.
1.1.2.1 General Behavior
A terminal loopback tests a circuit path as it passes through the XC-VXL cross-connect card loops back
from the card with the loopback. Figure 1-4 shows a terminal loopback on an STM-N card. The test-set
traffic comes into the electrical card and goes through the cross-connect card to the STM-N card. The
terminal loopback on the STM-N card turns the signal around before it reaches the LIU and sends it back
through the cross-connect card to the E1-N-14 card. This test verifies that the cross-connect card and
terminal circuit paths are valid, but does not test the LIU on the STM-N card.
Figure 1-4 Terminal Loopback Path on an STM-N Card
In CTC, STM-N cards with terminal loopbacks show an icon (Figure 1-5). Loopback icons are not shown
on other cards in this release.
Figure 1-5 Terminal Loopback Indicator
Figure 1-6 shows a terminal loopback on an E1-N-14 electrical card. The test-set traffic comes in on the
STM-N card and goes through the cross-connect card to the E1-N-14 card. The terminal loopback on the
E1-N-14 card turns the signal around before it reaches the LIU and sends it back through the
cross-connect card to the STM-N card. This test verifies that the cross-connect card and terminal circuit
paths are valid, but does not test the LIU on the E1-N-14 card.
Figure 1-6 Terminal Loopback Process on an E1-N-14 Card
76177
STM-N
Test Set
XCE3-12
E3-12
Test Set
XC STM-N
78262
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