Cisco ONS 15454 Troubleshooting Manual page 3

Chapter 1 General Troubleshooting
Figure 1-2
DS-N
Caution Before performing a facility (line) loopback on an OC-N card, be sure the card contains at least two data
communications channel (DCC) paths to the node where the card is installed. A second DCC provides
a nonlooped path to log into the node after the loopback is applied, enabling you to remove the facility
loopback. Ensuring a second DCC is not necessary if you are directly connected to the ONS 15454
containing the loopback OC-N card.
A terminal loopback tests a circuit path as it passes through the cross-connect card (XC10G) and loops
back from the card with the loopback.
transponder, and muxponder loopbacks follow the same model.) The test-set traffic comes into the DS-N
card and goes through the cross-connect card to the OC-N card. The terminal loopback on the OC-N card
turns the signal around before it reaches the LIU and sends it back through the cross-connect card to the
DS-N card. This test verifies that the cross-connect card and terminal circuit paths are valid, but does
not test the LIU on the OC-N card.
Setting a terminal loopback on the G-Series card might not 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 transmit (Tx) laser but on the Tx signal inside the G-Series card. In normal in-service
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.
Figure 1-3
Test Set
November 2004
Facility (Line) Loopback Process on an OC-N Card
XC OC-N
Test Set
Figure 1-3
Terminal Loopback Process on an OC-N Card
DS-N XC OC-N
1.1 Network Troubleshooting Tests
shows a terminal loopback on an OC-N card. (Ethernet,
Cisco ONS 15454 Troubleshooting Guide, R4.6
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