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Cisco IOS Software Configuration for the 1-Port Channelized OC-12/STM-4 (DS3) Line Card
How to Configure the 1-Port Channelized OC-12/STM-4 (DS3) Line Card
12
Cisco IOS Release 12.0(8)S
Using Loopback Commands
The 1-port channelized OC-12/STM-4 (DS3) line card supports loopback modes for both the OC-12
controller and for each of the associated DS3 channels. Specify the loopback mode by entering one of
the loopback interface configuration commands shown in Table 5. Use the no form of this command to
restore the default value, no loopback, which represents the normal operation between the local end
(TX) and the remote end (RX).
Figure 1 shows data flows for the various loopback modes.
Figure 1 Transmit and Receive Loopback Data Flows
OC-12 Controller Loopback Mode
The OC-12 controller supports two loopback modes:
• Internal—This loopback mode loops data from the transmit path to the receive path at the
mux/demux location on the line card, allowing diagnostics to send data to itself at the OC-12 level
without relying on external connections. In controller configuration mode, set the loopback mode to
internal, using the [no] loopback [internal | line ] configuration command:
Router(config-controller)# loopback internal
Router(config-controller)#
Use the no form of this command to restore the default value, no loopback.
Table 5 DS3 Supported Loopback Modes
Loopback modes Configuration Mode Command
Diagnostic or local loopback loopback local Router(config-if)# loopback local
Network loopback loopback network Router(config-if)# loopback
network
Remote loopback loopback remote Router(config-if)# loopback remote
Default value default value Router(config-if)# no loopback
Mux/
demux
Fiber
Line
loopback
OC-12
Internal loopback
STS-3
Internal loopback
OC-12
SUNI
622
STTX
Layer 3
routing
engine
11979