Cisco ONS 15454 Troubleshooting Manual page 7

Chapter 1 General Troubleshooting
1.2.1 Perform a Facility (Line) Loopback on a Source DS-N Port
The facility (line) loopback test is performed on the node source port in the network circuit, in this
example, the DS-N port in the source node. Completing a successful facility (line) loopback on this port
isolates the cabling, the DS-N card, and the EIA as possible failure points.
of a facility loopback on a source DS-N port.
Figure 1-8
Test Set
A hairpin circuit brings traffic in and out on a DS-N port rather than sending the traffic onto the OC-N
card. A hairpin loops back only the specific STS or VT circuit and does not cause an entire OC-N port
to loop back, thus preventing a drop of all traffic on the OC-N port. The hairpin allows you to test a
specific STS or VT circuit on nodes running live traffic.
a DS-N card.
Figure 1-9
Test Set
A cross-connect loopback tests a circuit path as it passes through the cross-connect card and loops back
to the port being tested. Testing and verifying circuit integrity often involves taking down the whole line;
however, a cross-connect loopback allows you to create a loopback on any embedded channel at
supported payloads at the STS-1 granularity and higher. For example, you can loop back a single STS-1,
STS-3c, STS-6c, etc. on an optical facility (line) without interrupting the other STS circuits.
The following restrictions apply to cross-connect loopbacks:
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November 2004
A Facility (Line) Loopback on a Circuit Source DS-N Port
Source
ONS Node
DS-N
Hairpin Circuit Process on a DS-N Card
DS-N
You can create a cross-connect loopback on all working or protect optical ports unless the protect
port is used in a 1+1 protection group and is in working mode.
If a terminal or facility loopback exists on a port, you cannot use the cross-connect loopback.
1.2.1 Perform a Facility (Line) Loopback on a Source DS-N Port
XC OC-N
Figure 1-9
XC OC-N
Cisco ONS 15454 Troubleshooting Guide, R4.6
Figure 1-10 shows an example
Destination
ONS Node
OC-N XC DS-N
shows the hairpin circuit process on
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