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Cisco ONS 15454 Troubleshooting Guide, R8.5
November 2009
Chapter 1 General Troubleshooting
1.1.1 Facility Loopbacks
Caution Ensure that the facility being loopbacked is not line-timing the node. If it is, a timing loop will be
created.
Note CTC sometimes refers to facility loopbacks as facility (line) loopbacks. “Line” is meant to clarify that
the loopback signal travels away from the facility where it originates and outward toward the span.
1.1.1.2 ONS 15454 Card Behavior
ONS 15454 port loopbacks either terminate or bridge the loopback signal. All ONS 15454 optical,
electrical, Ethernet, and FC_MR-4 facility loopbacks are terminated as shown in Table 1-1.
When a port terminates a facility loopback signal, the signal only loops back to the originating port and
is not transmitted downstream. When a port bridges a loopback signal, the signal loops back to the
originating port and is also transmitted downstream.
Note In Table 1-1, no alarm indication signal (AIS) is injected if the signal is bridged. If the signal is
terminated, an applicable AIS is injected downstream for all cards except Ethernet cards.
The loopback itself is listed in the Conditions window; for example, the Conditions window would list
the LPBKFACILITY condition for a tested port. (The Alarms window will show AS-MT, which means
that alarms are suppressed on the facility during loopback.)
The following behaviors also occur during loopback:
• If an electrical or optical port is in the Out-of-Service and Management, Disabled
(OOS-MA,DSBLD) service state, the port injects an AIS signal upstream and downstream.
• When an electrical or optical port is placed in the OOS-MA,MT service state before loopback
testing, the port clears the AIS signal upstream and downstream unless there is a service-affecting
defect that causes an AIS signal to be injected. For more information about placing ports into
alternate states for testing, refer to the “Change Card Settings” chapter in the Cisco ONS 15454
Procedure Guide.
Table 1-1 ONS 15454 Card Facility Loopback Behavior
Card/Port Facility Loopback Signal
DS-1 Terminated
DS-3 Terminated
DS3XM-6 or DS3XM-12 Terminated
All OC-N cards Terminated
EC-1 Terminated
G-Series Ethernet Terminated
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1. G-Series facility loopback is terminated and no AIS is sent downstream. However,
the Cisco Link Integrity signal continues to be sent downstream.
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