Cross-Connect (Xc) Loopbacks - Cisco ONS 15600 SDH Troubleshooting Manual

Chapter 1 General Troubleshooting
Figure 1-3
Test Set
The loopback is listed in the Conditions window. For example, the window would list the
LPBKTERMINAL condition or LPBKFACILITY condition for a tested port. (The Alarms window
would show AS-MT, which indicates that all alarms are suppressed on the port during loopback testing.)
In addition to the Conditions window listing, the following behaviors occur:
•
•
A lockout of protection must be executed before putting a two-fiber or four-fiber MS-SP Ring span into
Caution
a terminal loopback state. That is, a span lockout of one side (such as the east side) of a two-fiber MS-SP
Ring is required before operating a facility loopback on the same (east) side of the ring. A span lockout
of one protection side (such as the east protection side) of a four-fiber MS-SP Ring is required before
operating a terminal loopback on the same (east) side working line of the ring. If you do not execute the
lockout prior to creating the loopback, the ring can become stuck in an anomalous state after you release
the loopback.

1.1.4 Cross-Connect (XC) Loopbacks

An XC loopback tests an SDH virtual container (VC) circuit path as it passes through an SSXC card and
loops back to the port being tested without affecting other traffic on the optical port. Cross-connect
loopbacks are less invasive than terminal or facility loopbacks. Testing with facility or terminal
loopbacks often involve taking down the whole line; however, an XC loopback allows you to create a
loopback on any embedded channel at supported payloads of VC3 granularity and higher. For example,
you can place a loopback on a single VC3, VC4, VC4-2c, etc. on an optical facility without interrupting
the other VC circuits.
July 2010
Terminal Loopback on an STM-N Card with Bridged Signal
Source
ONS Node
STM-N XC
If an electrical or optical port is in the Locked-enabled,disabled service state, it injects an AIS signal
upstream and downstream.
When an optical or Ethernet port is placed in the Locked-enabled, maintenance service state before
loopback testing, the port clears the AIS signal upstream and downstream unless there is a
service-affecting defect that would also cause an AIS signal to be injected. For more information
about placing ports into alternate states for testing, refer to the "Change Card Settings" chapter of
the Cisco ONS 15600 SDH Procedure Guide.
Figure 1-4
STM-N STM-N
shows the XC loopback path.
Cisco ONS 15600 SDH Troubleshooting Guide, R8.0
1.1.4 Cross-Connect (XC) Loopbacks
Destination
ONS Node
XC STM-N
Test Set
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