Cisco Systems OC-12/STM-14 manual Using Loopback Commands, OC-12 Controller Loopback Mode

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

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).

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

Figure 1 shows data flows for the various loopback modes.

Figure 1 Transmit and Receive Loopback Data Flows

Internal loopback

OC-12

Fiber	Mux/	STTX
	demux

Line

loopback

OC-12

Internal loopback
STS-3
SUNI	Layer 3
	routing
622
	engine
	11979

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.

Cisco IOS Release 12.0(8)S

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