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Chapter 1
General Troubleshooting
Figure 1-8
Terminal Loopback on an STM-N Card with Bridged Signal
STM-N
Test Set
G-Series Ethernet cards placed in terminal loopback have different performance monitoring behavior
from other ONS 15454 SDH cards. (For more information about performance monitoring counters, see
the
stop the Tx Packets counter or the Rx Packet counters on the CTC card-level view Performance >
Statistics page from increasing. The counters can increment even though the loopbacked port has
temporarily disabled the transmit laser and is dropping any received packets.
The Tx Packet statistic continues to increment because the statistic is not based on the packets
transmitted by the Tx laser but on the Tx signal inside the G-Series card. In normal Unlocked-enabled
port operation, the Tx signal being recorded does result in the Tx laser transmitting packets, but in a
terminal loopback this signal is being looped back within the G-Series card and does not result in the Tx
laser transmitting packets.
The Rx Packet counter might also continue to increment when the G-Series card is in terminal loopback.
Receive (Rx) packets from any connected device are dropped and not recorded, but the internally looped
back packets follow the G-Series card's normal receive path and register on the Rx Packet counter.
MXP and TXP card facility loopbacks have different service state behaviors and requirements from other
ONS 15454 SDH cards. The cards can simultaneously maintain different service states. The following
behaviors also occur:
•
•
•
The loopback itself 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 will
show AS-MT, which means that alarms are suppressed on the facility during loopback.)
In addition to the Conditions window listing, the following behaviors occur:
•
•
July 2005
Source
ONS Node
XC
STM-N
Chapter 4, "Performance
Monitoring.") Setting a terminal loopback on the G-Series card might not
For TXP and TXPP client-side facility loopback, the client port is in the
Locked-enabled,maintenance & loopback service state and the trunk port must be in
Unlocked-enabled service state.
For MXP and MXPP cards with a client-side terminal loopback the client port is in the
Locked-enabled,maintenance & loopback service state and remaining client and trunk ports can be
in any service state.
In MXP or TXP trunk-side terminal loopbacks, the trunk port is in the Locked-enabled,maintenance
& loopback service state and the client ports must be in Unlocked-enabled service state for complete
loopback functionality. A facility loopback affects all client ports because it is performed on the
aggregate signal.
If an electrical or optical port is in the Locked-enabled,disabled service state, it injects an AIS signal
upstream and downstream.
When an electrical or optical 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 Cisco ONS 15454 SDH Procedure
Guide Chapter 5, "Turn Up Network."
Destination
ONS Node
STM-N
XC
STM-N
Cisco ONS 15454 SDH Troubleshooting Guide, R5.0
1.1.2 Terminal Loopbacks
Test Set
1-7
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