User Manual

Cisco High-Density Analog Voice and Fax Network Module

Configuration Tasks

Cisco IOS Release 12.2(2)XT and 12.2(8)T

Configuring Echo Adjustment

By design, echo cancellers are limited by the total amount of time they wait for the reflected speech to

be received, which is known as an echo trail. The echo trail is normally 32 milliseconds. In Cisco System

voice implementations, echo cancellers are enabled using the echo-cancel enable command, and echo

trails are configured using the echo-cancel coverage command.

To configure parameters related to the echo canceller, use the following commands beginning in

voice-port configuration mode:

Configuring Voice Level Adjustment

Use the input gain and output attenuation commands to adjust voice levels, and the impedance

command to set the impedance value to match that of the voice circuit to which the voice port connects.

To change parameters related to voice levels, use the following commands as appropriate, in voice-port

configuration mode:

Command Purpose

Step 1

Router(config-voiceport)# echo-cancel enable

Enables the cancellation of voice that is sent and

received on the same interface. Echo cancellation

coverage must also be configured. The default is

that echo cancellation is enabled.

Step 2

Router(config-voiceport)# echo-cancel coverage {8 | 16

| 24 | 32}

Adjusts the echo canceller by the specified number

of milliseconds. The default is 16.

Step 3

Router(config-voiceport)# non-linear

Enables nonlinear processing (residual echo

suppression) in the echo canceller, which shuts off

any signal if no near-end speech is detected. Echo

cancelling must be enabled for this feature. The

default is that nonlinear processing is enabled.

Command Purpose

Step 1

Router(config-voiceport)# input gain value

Specifies, in decibels, the amount of gain to be

inserted at the receiver side of the interface,

increasing or decreasing the signal. After an input

gain setting is changed, the voice call must be

disconnected and reestablished before the changes

take effect. The value argument is any integer from

–6 to 14. The default is 0.